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What is a chloroplast?

A chloroplast is an organelle within the cells of plants and certain algae that is the site of photosynthesis, which is the process by which energy from the Sun is converted into chemical energy for growth. A chloroplast is a type of plastid (a saclike organelle with a double membrane) that contains chlorophyll to absorb light energy.

Where are chloroplasts found?

Chloroplasts are present in the cells of all green tissues of plants and algae. Chloroplasts are also found in photosynthetic tissues that do not appear green, such as the brown blades of giant kelp or the red leaves of certain plants. In plants, chloroplasts are concentrated particularly in the parenchyma cells of the leaf mesophyll (the internal cell layers of a leaf).

Why are chloroplasts green?

Chloroplasts are green because they contain the pigment chlorophyll, which is vital for photosynthesis. Chlorophyll occurs in several distinct forms. Chlorophylls a and b are the major pigments found in higher plants and green algae.

Do chloroplasts have DNA?

Unlike most other organelles, chloroplasts and mitochondria have small circular chromosomes known as extranuclear DNA. Chloroplast DNA contains genes that are involved with aspects of photosynthesis and other chloroplast activities. It is thought that both chloroplasts and mitochondria are descended from free-living cyanobacteria, which could explain why they possess DNA that is distinct from the rest of the cell.


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chloroplast, structure within the cells of plants and green algae that is the site of photosynthesis, the process by which light energy is converted to chemical energy, resulting in the production of oxygen and energy-rich organic compounds. Photosynthetic cyanobacteria are free-living close relatives of chloroplasts; endosymbiotic theory posits that chloroplasts and mitochondria (energy-producing organelles in eukaryotic cells) are descended from such organisms.

Characteristics of chloroplasts

Learn about the structure of chloroplast and its role in photosynthesis

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Chloroplasts are a type of plastid—a round, oval, or disk-shaped body that is involved in the synthesis and storage of foodstuffs. Chloroplasts are distinguished from other types of plastids by their green colour, which results from the presence of two pigments, chlorophyll a and chlorophyll b. A function of those pigments is to absorb light energy for the process of photosynthesis. Other pigments, such as carotenoids, are also present in chloroplasts and serve as accessory pigments, trapping solar energy and passing it to chlorophyll. In plants, chloroplasts occur in all green tissues, though they are concentrated particularly in the parenchyma cells of the leaf mesophyll.

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Dissect a chloroplast and identify its stroma, thylakoids, and chlorophyll-packed grana

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Chloroplasts are roughly 1–2 μm (1 μm = 0.001 mm) thick and 5–7 μm in diameter. They are enclosed in a chloroplast envelope, which consists of a double membrane with outer and inner layers, between which is a gap called the intermembrane space. A third, internal membrane, extensively folded and characterized by the presence of closed disks (or thylakoids), is known as the thylakoid membrane. In most higher plants, the thylakoids are arranged in tight stacks called grana (singular granum). Grana are connected by stromal lamellae, extensions that run from one granum, through the stroma, into a neighbouring granum. The thylakoid membrane envelops a central aqueous region known as the thylakoid lumen. The space between the inner membrane and the thylakoid membrane is filled with stroma, a matrix containing dissolved enzymes, starch granules, and copies of the chloroplast genome.

The photosynthetic machinery

The thylakoid membrane houses chlorophylls and different protein complexes, including photosystem I, photosystem II, and ATP (adenosine triphosphate) synthase, which are specialized for light-dependent photosynthesis. When sunlight strikes the thylakoids, the light energy excites chlorophyll pigments, causing them to give up electrons. The electrons then enter the electron transport chain, a series of reactions that ultimately drives the phosphorylation of adenosine diphosphate (ADP) to the energy-rich storage compound ATP. Electron transport also results in the production of the reducing agent nicotinamide adenine dinucleotide phosphate (NADPH).

ATP and NADPH are used in the light-independent reactions (dark reactions) of photosynthesis, in which carbon dioxide and water are assimilated into organic compounds. The light-independent reactions of photosynthesis are carried out in the chloroplast stroma, which contains the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco). Rubisco catalyzes the first step of carbon fixation in the Calvin cycle (also called Calvin-Benson cycle), the primary pathway of carbon transport in plants. Among so-called C4 plants, the initial carbon fixation step and the Calvin cycle are separated spatially—carbon fixation occurs via phosphoenolpyruvate (PEP) carboxylation in chloroplasts located in the mesophyll, while malate, the four-carbon product of that process, is transported to chloroplasts in bundle-sheath cells, where the Calvin cycle is carried out. C4 photosynthesis attempts to minimize the loss of carbon dioxide to photorespiration. In plants that use crassulacean acid metabolism (CAM), PEP carboxylation and the Calvin cycle are separated temporally in chloroplasts, the former taking place at night and the latter during the day. The CAM pathway allows plants to carry out photosynthesis with minimal water loss.

Chloroplast genome and membrane transport

The chloroplast genome typically is circular (though linear forms have also been observed) and is roughly 120–200 kilobases in length. The modern chloroplast genome, however, is much reduced in size: over the course of evolution, increasing numbers of chloroplast genes have been transferred to the genome in the cell nucleus. As a result, proteins encoded by nuclear DNA have become essential to chloroplast function. Hence, the outer membrane of the chloroplast, which is freely permeable to small molecules, also contains transmembrane channels for the import of larger molecules, including nuclear-encoded proteins. The inner membrane is more restrictive, with transport limited to certain proteins (e.g., nuclear-encoded proteins) that are targeted for passage through transmembrane channels.

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One of the most widely recognized and important characteristics of plants is their ability to conduct photosynthesis, in effect, to make their own food by converting light energy into chemical energy. This process occurs in almost all plant species and is carried out in specialized organelles known as chloroplasts. All of the green structures in plants, including stems and unripened fruit, contain chloroplasts, but the majority of photosynthesis activity in most plants occurs in the leaves. On the average, the chloroplast density on the surface of a leaf is about one-half million per square millimeter.

Chloroplasts are one of several different types of plastids, plant cell organelles that are involved in energy storage and the synthesis of metabolic materials. The colorless leucoplasts, for instance, are involved in the synthesis of starch, oils, and proteins. Yellow-to-red colored chromoplasts manufacture carotenoids, and the green colored chloroplasts contain the pigments chlorophyll a and chlorophyll b, which are able to absorb the light energy needed for photosynthesis to occur. All plastids develop from tiny organelles found in the immature cells of plant meristems (undifferentiated plant tissue) termed proplastids, and those of a particular plant species all contain copies of the same circular genome. The disparities between the various types of plastids are based upon the needs of the differentiated cells they are contained in, which may be influenced by environmental conditions, such as whether light or darkness surrounds a leaf as it grows.

The ellipsoid-shaped chloroplast is enclosed in a double membrane and the area between the two layers that make up the membrane is called the intermembrane space. The outer layer of the double membrane is much more permeable than the inner layer, which features a number of embedded membrane transport proteins. Enclosed by the chloroplast membrane is the stroma, a semi-fluid material that contains dissolved enzymes and comprises most of the chloroplast’s volume. Since, like mitochondria, chloroplasts possess their own genomes (DNA), the stroma contains chloroplast DNA and special ribosomes and RNAs as well. In higher plants, lamellae, internal membranes with stacks (each termed a granum) of closed hollow disks called thylakoids, are also usually dispersed throughout the stroma. The numerous thylakoids in each stack are thought to be connected via their lumens (internal spaces).

Light travels as packets of energy called photons and is absorbed in this form by light-absorbing chlorophyll molecules embedded in the thylakoid disks. When these chlorophyll molecules absorb the photons, they emit electrons, which they obtain from water (a process that results in the release of oxygen as a byproduct). The movement of the electrons causes hydrogen ions to be propelled across the membrane surrounding the thylakoid stack, which consequently initiates the formation of an electrochemical gradient that drives the stroma’s production of adenosine triphosphate (ATP). ATP is the chemical energy «currency» of the cell that powers the cell’s metabolic activities. In the stroma, the light-independent reactions of photosynthesis, which involve carbon fixation, occur, and low-energy carbon dioxide is transformed into a high-energy compound like glucose.

Plant cells are remarkable in that they have two organelles specialized for energy production: chloroplasts, which create energy via photosynthesis, and mitochondria, which generate energy through respiration, a particularly important process when light is unavailable. Like the mitochondrion, the chloroplast is different from most other organelles because it has its own DNA and reproduces independently of the cell in which it is found; an apparent case of endosymbiosis. Scientists hypothesize that millions of years ago small, free-living prokaryotes were engulfed, but not consumed, by larger prokaryotes, perhaps because they were able to resist the digestive enzymes of the engulfing organism. According to DNA evidence, the eukaryotic organisms that later became plants likely added the photosynthetic pathway in this way, by acquiring a photosynthetic bacterium as an endosymbiont.

As suggested by this hypothesis, the two organisms developed a symbiotic relationship over time, the larger organism providing the smaller with ample nutrients and the smaller organism providing ATP molecules to the larger one. Eventually, the larger organism developed into the eukaryotic cell, the smaller organism into the chloroplast. Nonetheless, there are a number of prokaryotic traits that chloroplasts continue to exhibit. Their DNA is circular, as it is in the prokaryotes, and their ribosomes and reproductive methods (binary fission) are more like those of the prokaryotes.


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Chloroplasts are the food producers of the cell. The organelles are only found in plant cells and some protists such as algae. Animal cells do not have chloroplasts. Chloroplasts work to convert light energy of the Sun into sugars that can be used by cells. The entire process is called photosynthesis and it all depends on the little green chlorophyll molecules in each chloroplast.

Plants are the basis of all life on Earth. They are classified as the producers of the world. In the process of photosynthesis, plants create sugars and release oxygen (O2). The oxygen released by the chloroplasts is the same oxygen you breathe every day. Mitochondria work in the opposite direction. They use oxygen in the process of releasing chemical energy from sugars.

We’ll hit the high points for the structure of a chloroplast. Two membranes contain and protect the inner parts of the chloroplast. They are appropriately named the outer and inner membranes. The inner membrane surrounds the stroma and the grana (stacks of thylakoids). One thylakoid stack is called a granum.

Chlorophyll molecules sit on the surface of each thylakoid and capture light energy from the Sun. As energy rich molecules are created by the light-dependent reactions, they move to the stroma where carbon (C) can be fixed and sugars are synthesized.

The stacks of thylakoid sacs are connected by stroma lamellae. The lamellae act like the skeleton of the chloroplast, keeping all of the sacs a safe distance from each other and maximizing the efficiency of the organelle. If all of the thylakoids were overlapping and bunched together, there would not be an efficient way to capture the Sun’s energy.

The purpose of the chloroplast is to make sugars that feed the cell’s machinery. Photosynthesis is the process of a plant taking energy from the Sun and creating sugars. When the energy from the Sun hits a chloroplast and the chlorophyll molecules, light energy is converted into the chemical energy found in compounds such as ATP and NADPH.

Those energy-rich compounds move into the stroma where enzymes fix the carbon atoms from carbon dioxide (CO2). The molecular reactions eventually create sugar and oxygen (O2). Plants and animals then use the sugars (glucose) for food and energy. Animals also breathe the oxygen gas that is released.

Not all chlorophyll is the same. Several types of chlorophyll can be involved in photosynthesis. You will hear about chlorophyll a and b most often. All chlorophylls are varieties of green and have a common chemical structure called a porphyrin ring.

There are other molecules that are also photosynthetic. One day you might hear about carotenoids in carrots, phycocyanin in bacteria, phycoerythrin in algae, or fucoxanthin in brown algae. While these compounds might be involved in photosynthesis, they are not all green or the same structure as chlorophyll. Accessory pigments such as carotenoids and fucoxanthin pass absorbed light energy to neighboring chlorophyll molecules instead of using it themselves.


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Organelle Components and Photosynthesis Basics

Posted on 3/18/22 by Sarah Boudreau

Open up your refrigerator—all the delicious things you see in there have either relied on photosynthesis or have eaten something that relies on photosynthesis. During photosynthesis, photosynthetic organisms synthesize sugar molecules from sunlight, water, and carbon dioxide.  Photosynthesis takes place in the chloroplasts of plant cells, so they’re the reason that plants (and some other organisms) can produce food on their own

Photosynthesis is important not only for individual organisms, it’s important for life on earth. Photosynthesis is part of the global carbon cycle: put simply, photosynthesis turns carbon dioxide into organic molecules, and respiration turns those molecules back into carbon dioxide. 

Shoutout to the chloroplast for making much of this happen! In today’s blog post, let’s explore the chloroplast and the process of photosynthesis. 

What is a chloroplast?

The chloroplast is a type of plastid; plastids are organelles with double membranes that are involved with the synthesis and storage of food. Other plastids include chromoplasts (which contain pigments other than green) and leucoplasts (which contain no pigments). 

Chloroplasts are filled with chlorophyll, that great green pigment that stains the knees of your jeans if you trip and fall on your lawn. Most algae, and a group of protists called Euglena, also have chloroplasts, and some bacteria (like cyanobacteria) have chlorophyll, but it’s not located in organelles. 

The chlorophyll in plants absorbs blue and red light and reflects green. The two most common types of chlorophyll are a and b. Chlorophyll a is in all chloroplasts, and the amount of other chlorophyll types is different depending on the species of plant.

Image from Visible Biology.

Interestingly, chloroplasts have their own DNA. This is likely because, like mitochondria, they once existed separately from the cell. Chloroplasts were most likely prokaryotic cells that were encompassed by larger eukaryotic cells and evolved into organelles. It’s not a coincidence that chloroplast DNA is small and circular, like bacterial DNA. 

There are many chloroplasts throughout the cytoplasm of photosynthetic cells: these cells can have anywhere from one to one hundred chloroplasts that divide to replicate themselves.  

Parts of the chloroplast

The chloroplast has three membrane systems: the outer membrane, the inner membrane, and the thylakoid system. 

Thylakoids are disc-shaped and collect photons from a light source (usually the sun). They consist of a thylakoid membrane that surrounds the lumen. The lumen is where processes like oxygen evolution, plastocyanin-mediated electron transfer, and photoprotection occur during photosynthesis. Proteins in the lumen contribute to many other processes, including turnover of photosynthetic protein complexes. Thylakoids are arranged in stacks called grana (singular granum). 

The lumen (highlighted in blue). Image from Visible Biology.

Between the inner membrane and the grana lies the stroma, a thick, protein-rich fluid. This is where the light-independent reactions of photosynthesis take place—but we’ll hear more about that soon! 

The basics of photosynthesis 

In brief, photosynthesis requires carbon dioxide, water, and sunlight and produces glucose and oxygen.

Learn more about what goes in and what comes out of photosynthesis with this Visible Biology Bite. 

The process of photosynthesis has two main kinds of reactions: light-dependent reactions and light-independent reactions. Light-dependent reactions convert light into stored energy, and light-independent reactions use that energy to assemble glucose. 

We’ll give you the run-down on both of these categories. 

Light-dependent reactions

Light-dependent reactions take place in the thylakoid membrane. In these reactions, the organism absorbs sunlight, breaks down water molecules, puts together ATP and NADPH molecules to store energy, and releases oxygen.  

Sunlight hits the chlorophyll within the thylakoid membrane, causing an electron to become excited and leave the chlorophyll molecule. When the electron leaves, it creates a vacuum in its wake. Photosystem II then splits a water molecule to restore the electron. Photosystems are complexes of proteins and pigments— we’ll hear about photosystem I soon. 

Photosystem II (highlighted in blue), water molecules being broken down, and electrons moving along to photosystem I. Image from Visible Biology.


Once the water molecule has been broken down, it contributes to the building of ATP: its hydrogen ions help the ATP synthase enzyme add a phosphate group to ADP. The leftover oxygen atom combines with another oxygen atom to form O₂, and the oxygen gas is released through openings in the leaves. 

Remember that electron that left the chlorophyll molecule? It moves along the thylakoid membrane until it reaches photosystem I. It combines with another excited electron, and an enzyme adds that plus a hydrogen atom to NADP to create NADPH, a molecule that stores energy.  

Ta da! Light-dependent reactions convert energy from sunlight into chemical energy.

Light-independent reactions (aka the Calvin cycle)

Light-independent reactions, on the other hand, don’t need light directly. Also called the Calvin cycle, light-independent reactions use the stored energy from the light-dependent reactions to alter the carbon from carbon dioxide so it can be used to build carbohydrates like glucose. These reactions take place in the stroma.

Stroma highlighted in blue. Image from Visible Biology.

During light-independent reactions, an enzyme combines a molecule of carbon dioxide with a molecule called ribulose biphosphate (RuBP). The resulting 6-carbon molecule is broken down into two 3-carbon molecules. Then, each of those 3-carbon molecules (called 3-phosphoglycerate or 3-PGA) is given a hydrogen atom, creating glyceraldehyde-3-phosphate, aka G3P.

G3P can be used to build sugars—combine two molecules of G3P and what do you get? Glucose!

The Calvin cycle produces twelve G3P molecules: two of those are used for glucose and the other ten are recycled into RuBP. Then the cycle can continue, creating more and more glucose.

Plants use glucose in many different ways. First and foremost, it’s a source of energy. It’s also used to make cellulose, the primary building material of plants. Glucose can also attach to proteins and lipids to make them more soluble. 


The chloroplast is a plastid that is made up of an outer membrane, an inner membrane, grana, and the stroma. It’s within the chloroplast that photosynthesis takes place in plants, turning sunlight and carbon dioxide into sugar and oxygen. The chloroplast and the chlorophyll within it are the reason plants can make their own energy without having to consume other organisms. 

If you’re looking for a way to teach photosynthesis, check out this free photosynthesis lesson plan. 

If you’re interested in learning more about photosynthesis and how it differs from cellular respiration, check out this blog post! 


Be sure to subscribe to the Visible Body Blog for more anatomy awesomeness! 

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Chloroplast — Definition and Examples

n., Synonyms: chloroplastid; green plastid; chloroleucite
Chloroplast definition: A plastid that contains high amounts of chlorophyll and where photosynthesis takes place

Table of Contents

Chloroplast Definition

What is chloroplast? In biology, a chloroplast refers to the organelle found within the cell of plants and other photosynthetic eukaryotes that is filled with the green pigment called chlorophyll. Etymology: from Greek “chloros”, meaning “green” and “plast”, meaning “form” or “entity”. Synonyms: chloroplastid; green plastid; chloroleucite.

When a eukaryote possesses chloroplasts, it indicates that it has the capacity to produce its own food. It does so through photosynthesis. Which types of cells contain chloroplasts? Plants are examples of organisms that possess chloroplasts inside their cells. Taking a look at their cells will reveal the presence of numerous chloroplasts that spread throughout the cytoplasm (see leaf anatomy picture below). Each chloroplast contains a light-harvesting system containing chlorophylls. These green pigments absorb light in the blue and red of the electromagnetic spectrum. They, however, reflect the green portion of the spectrum. It is for this reason that plants are green. By contrast, animal cells do not contain chloroplasts. Thus, apart from the presence of a cell wall (i.e. a layer made up of cellulose and accounts for cell rigidity in plants), the presence of chloroplasts is another defining characteristic that could help identify plants from the animals. Other organisms that possess chloroplasts are the eukaryotic algae, e.g. green algae. Some bacteria that are photosynthetic (e.g. phototrophs and cyanobacteria) have chlorophylls in their cells. However, their chlorophylls will not be found inside a double membraned organelle such as the chloroplast. Rather, the chlorophyll pigments are located in the thylakoid membrane of a bacterial cell.

Plant leaf anatomy. Notice the numerous chloroplasts inside the cells of a leaf. (Image credit: Zephyris, CC BY-SA 3.0)

Characteristics of Chloroplast

The chloroplast is one of the organelles of a photosynthetic eukaryotic cell. It is a type of plastid (the other types are chromoplasts and leucoplasts). The chloroplasts are identifiable from the other plastids by their color, shape, structure, and function. The chloroplasts are green due to the chlorophyll pigments that occur in abundance. The two most common types are chlorophyll a and b. Other chlorophyll pigments are chlorophyll c, d, and f. Chlorophyll a is present in all chloroplasts whereas the other types are present (in varying amounts) depending on the species. In vascular plants, the shape resembles a lens or a disc and the size, approximately 5µm in length and ~2.5µm in width. (Ref.1) In algae, the shape may vary. They could be round, oval, or tubular.

Structure of Chloroplast

What is the structure of chloroplast? The chloroplast has at least three membrane systems: (1) outer membrane, (2) inner membrane, and (3) thylakoid system. The outer and inner membranes are the double membrane system that is a typical feature of an organelle. The thylakoids are disk-shaped structures that perform the role of harvesting or collecting photons from a light source, such as the sunlight. Embedded in the thylakoid membrane is the antenna complex consisting of proteins, and light-absorbing pigments, particularly chlorophyll and carotenoids. Hence, the job of the thylakoid is to provide a site for the light reactions of photosynthesis. The stack of thylakoids (resembling a stack of coins) is called granum (plural: grana). The matrix of the chloroplast is referred to as the stroma. It is the thick fluid in between grana. It contains enzymes, molecules, and ions. It is where the light-independent process of sugar formation takes place (the dark reactions of photosynthesis).

Similar to the mitochondria, the chloroplasts are semi-autonomous organelles. They possess their own DNA, which is referred to as chloroplast DNA or cpDNA. Thus, they do not solely rely on the genes contained in the nucleus. They produce certain proteins from their own DNA. (Ref.2)

Chloroplast with labeled parts. Credit: Vossman, CC BY-SA 4.0.

Chloroplast Functions

What is the function of the chloroplast? Chloroplasts carry out the process of photosynthesis. Their main role is to provide the site for light and dark reactions. Through these organelles, inorganic sources, water, and light energy are converted into food, i.e. glucose (a sugar molecule). They are, therefore, important to photosynthetic organisms for the purpose of producing food on their own and not needing to feed on other organisms to survive. Because oxygen is one of the byproducts of photosynthesis, the chloroplasts are therefore a crucial site for producing such gas, which later is released from the cell into the environment. Oxygen is biologically important for its role, in turn, in various biochemical and physiological processes in animals.

For further description and facts on photosynthesis, read Plant Metabolism tutorial.

Chloroplast Evolution

The Endosymbiotic theory was conceptualized to delineate the origin of chloroplasts. (Ref.3) Accordingly, organelles such as mitochondria and chloroplasts were cellular structures in eukaryotic cells that emerged as a result of a primary endosymbiosis that took place millions of years ago between the prokaryotic endosymbionts and the eukaryotic host cells. The eukaryotic cell, being the larger cell, took in the smaller photosynthetic prokaryotes (e.g. cyanobacteria) that consequently enabled them to photosynthesize. Eventually, the prokaryotes evolved and differentiated into plastids, particularly, chloroplasts. These early photosynthetic eukaryotes harboring prokaryotes-turned-organelles are presumed to be the early ancestors of modern plants and algae on Earth. The discovery of the cpDNA in chloroplasts, the similarity in membranes, and the binary fission as a means of reproduction serve as evidence that supports this theory. (Ref.4)

Read also:
What is the Likely Origin of Chloroplasts? – BioTechniques. (2017, December 14). BioTechniques. https://www.biotechniques.com/molecular-biology/when-did-the-chloroplast-evolve/



See also

  • Chlorophyll
  • Etioplast
  • Chromoplast
  • Leucoplast
  • Plastid


  1. Staehelin, L. A. (2003). Chloroplast structure: from chlorophyll granules to supra-molecular architecture of thylakoid membranes. Photosynthesis Research, 76(1–3), 185–196. https://doi.org/10.1023/A:1024994525586
  2. Discovery of Chloroplast DNA, Genomes and Genes | Discoveries in Plant Biology. (2019). Worldscientific.Com. https://www.worldscientific.com/doi/abs/10.1142/9789812813046_0002
  3. Jensen, P. E., & Leister, D. (2014). Chloroplast evolution, structure and functions. F1000Prime Reports, 6. https://doi.org/10.12703/p6-40
  4. Evidence for endosymbiosis. (2020). Berkeley.Edu. https://evolution.berkeley.edu/evolibrary/article/_0_0/endosymbiosis_04

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Chloroplasts and Other Plastids — The Cell

Chloroplasts, the organelles responsible for photosynthesis, are in many respects similar to mitochondria. Both chloroplasts and mitochondria function to generate metabolic energy, evolved by endosymbiosis, contain their own genetic systems, and replicate by division. However, chloroplasts are larger and more complex than mitochondria, and they perform several critical tasks in addition to the generation of ATP. Most importantly, chloroplasts are responsible for the photosynthetic conversion of CO2 to carbohydrates. In addition, chloroplasts synthesize amino acids, fatty acids, and the lipid components of their own membranes. The reduction of nitrite (NO2) to ammonia (NH3), an essential step in the incorporation of nitrogen into organic compounds, also occurs in chloroplasts. Moreover, chloroplasts are only one of several types of related organelles (plastids) that play a variety of roles in plant cells.

The Structure and Function of Chloroplasts

Plant chloroplasts are large organelles (5 to 10 μm long) that, like mitochondria, are bounded by a double membrane called the chloroplast envelope (). In addition to the inner and outer membranes of the envelope, chloroplasts have a third internal membrane system, called the thylakoid membrane. The thylakoid membrane forms a network of flattened discs called thylakoids, which are frequently arranged in stacks called grana. Because of this three-membrane structure, the internal organization of chloroplasts is more complex than that of mitochondria. In particular, their three membranes divide chloroplasts into three distinct internal compartments: (1) the intermembrane space between the two membranes of the chloroplast envelope; (2) the stroma, which lies inside the envelope but outside the thylakoid membrane; and (3) the thylakoid lumen.

Figure 10.13

Structure of a chloroplast. In addition to the inner and outer membranes of the envelope, chloroplasts contain a third internal membrane system: the thylakoid membrane. These membranes divide chloroplasts into three internal compartments. (Electron micrograph (more…)

Despite this greater complexity, the membranes of chloroplasts have clear functional similarities with those of mitochondria—as expected, given the role of both organelles in the chemiosmotic generation of ATP. The outer membrane of the chloroplast envelope, like that of mitochondria, contains porins and is therefore freely permeable to small molecules. In contrast, the inner membrane is impermeable to ions and metabolites, which are therefore able to enter chloroplasts only via specific membrane transporters. These properties of the inner and outer membranes of the chloroplast envelope are similar to the inner and outer membranes of mitochondria: In both cases the inner membrane restricts the passage of molecules between the cytosol and the interior of the organelle. The chloroplast stroma is also equivalent in function to the mitochondrial matrix: It contains the chloroplast genetic system and a variety of metabolic enzymes, including those responsible for the critical conversion of CO2 to carbohydrates during photosynthesis.

The major difference between chloroplasts and mitochondria, in terms of both structure and function, is the thylakoid membrane. This membrane is of central importance in chloroplasts, where it fills the role of the inner mitochondrial membrane in electron transport and the chemiosmotic generation of ATP (). The inner membrane of the chloroplast envelope (which is not folded into cristae) does not function in photosynthesis. Instead, the chloroplast electron transport system is located in the thylakoid membrane, and protons are pumped across this membrane from the stroma to the thylakoid lumen. The resulting electrochemical gradient then drives ATP synthesis as protons cross back into the stroma. In terms of its role in generation of metabolic energy, the thylakoid membrane of chloroplasts is thus equivalent to the inner membrane of mitochondria.

Figure 10.14

Chemiosmotic generation of ATP in chloroplasts and mitochondria. In mitochondria, electron transport generates a proton gradient across the inner membrane, which is then used to drive ATP synthesis in the matrix. In chloroplasts, the proton gradient is (more…)

The Chloroplast Genome

Like mitochondria, chloroplasts contain their own genetic system, reflecting their evolutionary origins from photosynthetic bacteria. The genomes of chloroplasts are similar to those of mitochondria in that they consist of circular DNA molecules present in multiple copies per organelle. However, chloroplast genomes are larger and more complex than those of mitochondria, ranging from 120 to 160 kb and containing approximately 120 genes.

The chloroplast genomes of several plants have been completely sequenced, leading to the identification of many of the genes contained in the organelle DNAs. These chloroplast genes encode both RNAs and proteins involved in gene expression, as well as a variety of proteins that function in photosynthesis (). Both the ribosomal and transfer RNAs used for translation of chloroplast mRNAs are encoded by the organelle genome. These include four rRNAs (23S, 16S, 5S, and 4.5S) and 30 tRNA species. In contrast to the smaller number of tRNAs encoded by the mitochondrial genome, the chloroplast tRNAs are sufficient to translate all the mRNA codons according to the universal genetic code. In addition to these RNA components of the translation system, the chloroplast genome encodes about 20 ribosomal proteins, which represent approximately a third of the proteins of chloroplast ribosomes. Some subunits of RNA polymerase are also encoded by chloroplasts, although additional RNA polymerase subunits and other factors needed for chloroplast gene expression are encoded in the nucleus.

Table 10.2

Genes Encoded by Chloroplast DNA.

The chloroplast genome also encodes approximately 30 proteins that are involved in photosynthesis, including components of photosystems I and II, of the cytochrome bf complex, and of ATP synthase. In addition, one of the subunits of ribulose bisphosphate carboxylase (rubisco) is encoded by chloroplast DNA. Rubisco is the critical enzyme that catalyzes the addition of CO2 to ribulose-1,5-bisphosphate during the Calvin cycle (see ). Not only is it the major protein component of the chloroplast stroma, but it is also thought to be the single most abundant protein on Earth, so it is noteworthy that one of its subunits is encoded by the chloroplast genome.

Import and Sorting of Chloroplast Proteins

Although chloroplasts encode more of their own proteins than mitochondria, about 90% of chloroplast proteins are still encoded by nuclear genes. As with mitochondria, these proteins are synthesized on cytosolic ribosomes and then imported into chloroplasts as completed polypeptide chains. They must then be sorted to their appropriate location within chloroplasts—an even more complicated task than protein sorting in mitochondria, since chloroplasts contain three separate membranes that divide them into three distinct internal compartments.

Protein import into chloroplasts generally resembles mitochondrial protein import (). Proteins are targeted for import into chloroplasts by N-terminal sequences of 30 to 100 amino acids, called transit peptides, which direct protein translocation across the two membranes of the chloroplast envelope and are then removed by proteolytic cleavage. The transit peptides are recognized by the translocation complex of the chloroplast outer member (the Toc complex), and proteins are transported through this complex across the membrane. They are then transferred to the translocation complex of the inner membrane (the Tic complex) and transported across the inner membrane to the stroma. As in mitochondria, molecular chaperones on both the cytosolic and stromal sides of the envelope are required for protein import, which requires energy in the form of ATP. In contrast to the presequences of mitochondrial import, however, transit peptides are not positively charged and the translocation of polypeptide chains into chloroplasts does not require an electric potential across the membrane.

Figure 10.15

Protein import into the chloroplast stroma. Proteins are targeted for import into chloroplasts by a transit peptide at their amino terminus. The transit peptide directs polypeptide translocation through the Toc complex in the chloroplast outer membrane (more…)

Proteins incorporated into the thylakoid lumen are transported to their destination in two steps (). They are first imported into the stroma, as already described, and are then targeted for translocation across the thylakoid membrane by a second hydrophobic signal sequence, which is exposed following cleavage of the transit peptide. The hydrophobic signal sequence directs translocation of the polypeptide across the thylakoid membrane and is finally removed by a second proteolytic cleavage within the lumen.

Figure 10.16

Import of proteins into the thylakoid lumen. Proteins are imported into the thylakoid lumen in two steps. The first step is import into the chloroplast stroma, as illustrated in Figure 10.15. Cleavage of the transit peptide then exposes a second hydrophobic (more…)

The pathways of protein sorting to the other four compartments of chloroplasts—the inner and outer membranes, thylakoid membrane, and intermembrane space—are less well established. As with mitochondria, proteins appear to be inserted directly into the outer membrane of the chloroplast envelope. In contrast, proteins destined for either the thylakoid membrane or the inner membrane of the chloroplast envelope are initially targeted for import into the stroma by N-terminal transit peptides. Following cleavage of the transit peptides, these proteins are then targeted for insertion into the appropriate membrane by other sequences, which are not yet well characterized. Finally, neither the sequences that target proteins to the intermembrane space nor the pathways by which they travel to that destination have been identified.

Other Plastids

Chloroplasts are only one, albeit the most prominent, member of a larger family of plant organelles called plastids. All plastids contain the same genome as chloroplasts, but they differ in both structure and function. Chloroplasts are specialized for photosynthesis and are unique in that they contain the internal thylakoid membrane system. Other plastids, which are involved in different aspects of plant cell metabolism, are bounded by the two membranes of the plastid envelope but lack both the thylakoid membranes and other components of the photosynthetic apparatus.

The different types of plastids are frequently classified according to the kinds of pigments they contain. Chloroplasts are so named because they contain chlorophyll. Chromoplasts () lack chlorophyll but contain carotenoids; they are responsible for the yellow, orange, and red colors of some flowers and fruits, although their precise function in cell metabolism is not clear. Leucoplasts are nonpigmented plastids, which store a variety of energy sources in nonphotosynthetic tissues. Amyloplasts () and elaioplasts are examples of leucoplasts that store starch and lipids, respectively.

Figure 10.17

Electron micrographs of chromoplasts and amyloplasts. (A) Chromoplasts contain lipid droplets in which carote-noids are stored. (B) Amyloplasts contain large starch granules. (A, Biophoto Associates/Photo Researchers, Inc.; B, Dr. Jeremy Burgess/Photo (more…)

All plastids, including chloroplasts, develop from proplastids, small (0.5 to 1 μm in diameter) undifferentiated organelles present in the rapidly dividing cells of plant roots and shoots. Proplastids then develop into the various types of mature plastids according to the needs of differentiated cells. In addition, mature plastids are able to change from one type to another. Chromoplasts develop from chloroplasts, for example, during the ripening of fruit (e.g. , tomatoes). During this process, chlorophyll and the thylakoid membranes break down, while new types of carotenoids are synthesized.

An interesting feature of plastids is that their development is controlled both by environmental signals and by intrinsic programs of cell differentiation. In the photosynthetic cells of leaves, for example, proplastids develop into chloroplasts (). During this process, the thylakoid membrane is formed by vesicles budding from the inner membrane of the plastid envelope and the various components of the photosynthetic apparatus are synthesized and assembled. However, chloroplasts develop only in the presence of light. If plants are kept in the dark, the development of proplastids in leaves is arrested at an intermediate stage (called etioplasts), in which a semicrystalline array of tubular internal membranes has formed but chlorophyll has not been synthesized (). If dark-grown plants are then exposed to light, the etioplasts continue their development to chloroplasts. It is noteworthy that this dual control of plastid development involves the coordinated expression of genes within both the plastid and nuclear genomes. The mechanisms responsible for such coordinated gene expression are largely unknown, and their elucidation represents a challenging problem in plant molecular biology.

Figure 10.18

Development of chloroplasts. Chloroplasts develop from proplastids in the photosynthetic cells of leaves. Proplastids contain only the inner and outer envelope membranes; the thylakoid membrane is formed by vesicle budding from the inner membrane during (more…)

Figure 10.19

Electron micrograph of an etioplast. (John N. A. Lott/Biological Photo Service.)

What a chloroplast looks like — From Earth to Heaven

Meaning of the word Chloroplasts according to Efremova:

Chloroplasts — Green plastids of a plant cell containing chlorophyll, carotene and involved in the process of photosynthesis.

Chloroplasts in the Encyclopedic Dictionary:

Chloroplasts — (from Greek chloros — green and plastos — molded — formed), intracellular organelles of a plant cell in which photosynthesis is carried out. are colored green (they contain chlorophyll). Own genetic apparatus and protein-synthesizing system provide chloroplasts with relative autonomy. In the cell of higher plants from 10 to 70 X.

The meaning of the word Chloroplasts according to the Brockhaus and Efron dictionary:

Chloroplasts are bodies enclosed in plant cells, colored green and containing chlorophyll. In higher plants, X. have a very definite shape and are called chlorophyll grains (see). in algae their form is diverse and they are called chromatophores (see) or chlorophores. The basis of X. (stroma) is proteinaceous and protoplasmic. Their structure, especially the ratio of the pigment to the stroma, has not been completely elucidated, and the views of scientists on the structure of X. do not agree with each other.

TSB definition of the word «Chloroplast»:

Chloroplasts (from the Greek chlorus — green and plastus — fashioned, formed)
intracellular organelles of a plant cell — Plastids, in which photosynthesis is carried out. They are colored green due to the presence in them of the main pigment of photosynthesis — Chlorophyll. The main function of chlorine, which consists in capturing and converting light energy, is also reflected in the features of their structure. In higher plants, Ch. are lenticular bodies 3–10 μm in diameter and 2–5 μm thick; they are a system of protein-lipid membranes immersed in the main substance, the matrix, or stroma, and delimited from the cytoplasm by an outer membrane (sheath). The inner membranes form a single (continuous) lamellar, or lamellar, system consisting of closed flattened sacs (cistern) — the so-called. thylakoids, which are grouped by 10-30 (stacks) into grana (up to 150 in X.), interconnected by large thylakoids. With such a structure, the photoactive surface of the crystal increases significantly and the maximum use of light energy is ensured.
In the thylakoid membrane, consisting of two layers of protein separated by a layer of lipids, the primary light stage of photosynthesis takes place, leading to the formation of two compounds necessary for the assimilation of CO 2 — reduced nicotinamide adenine dinucleotide phosphate (NADP H) and an energy-rich compound adenosine triphosphate (ATP ).

The source of energy for the formation of ATP molecules is the potential difference that is formed on the membrane as a result of vector (directed) charge transfer. The charge separation on both sides of the membrane is ensured by the special arrangement of the components of the electron transport chain in the membrane, which lace up its thickness. Thanks to the membranes that play the role of
«partitions», the spatial separation of photosynthesis products is carried out, for example, O 2 and reducing agents, without which these products would interact with each other. The outer surface of the thylakoid is covered with particles with a diameter of 14-15 nm, which are
«coupling factors», involved in the synthesis of ATP. In the stroma, the fixation enzymes CO 2 are concentrated. (dark stage of photosynthesis).
In plants capable of «cooperative» photosynthesis, there are 2 types of Ch., differing in structure and functions. Some of them, located in the cells of the mesophyll, are small with grana, others, larger, are contained in the cells of the lining of the conducting vascular bundles, the grana in them are only rudimentary or completely absent. In Ch. of the second type, photosystem 1 functions, which forms ATP in the course of cyclic phosphorylation, and NADP H — due to the decarboxylation reaction of malic acid.

labels of the lining fix CO 2 on ribulose diphosphate, i.e., using the Calvin cycle, and mesophyll cells on phosphoenolpyruvate (the Hatch-Slack pathway). then. The interaction of both types of chlorophyll ensures the high efficiency of photosynthesis in plants. In addition to the CO 2 fixation enzymes, the H. stroma includes DNA strands, ribosomes, starch granules, and osmiophilic granules.
The presence in Ch. of its own genetic apparatus and a specific protein-synthesizing system determines a certain, albeit relative, autonomy of Ch. in the cell. During the development and reproduction of plants in new generations of cells, chlorophyll occurs only by division. The origin of Ch. is associated with Symbiogenesis, suggesting that modern Ch. are the descendants of blue-green algae that entered into symbiosis with ancient nuclear heterotrophic cells of colorless algae or protozoa.
Ch. occupy 20-30% of the plant cell volume. Algae, such as chlamydomonas, have one Ch., while the cell of higher plants contains from 10 to 70 Ch. Chromium develops from the so-called. initial particles, or proplastids, are small vesicles that separate from the nucleus. At the end of the growing season, chlorophyll plants lose their green color as a result of the destruction of chlorophyll and turn into chromoplasts. See also Photosynthesis.
Lit.: Chloroplasts and mitochondria. Questions of membrane biology, Sat., M., 1969. Levi A., Sikevits F., Structure and function of the cell, trans. from English, M., 1971. Heath O., Photosynthesis, trans. from English, M., 1972. Baslavskaya S. S., Photosynthesis, M., 1974. Nasyrov Yu. S., Photosynthesis and genetics of chloroplasts, M., 1975. Structure and function orchloroplasts, ed. M. Gibbs, B., 1971.
R. M. Bekina.
Micrograph of a chloroplast.
Model of lamellar (lamellar) system of chloroplasts. Columns are grana formed by thylakoids.


Source: xn—-7sbbh7akdldfh0ai3n.xn--p1ai

Source: www.chem21.info


At present, [2] the origin of chloroplasts by symbiogenesis is generally recognized. It is assumed that chloroplasts originated from cyanobacteria, since they are a two-membrane organoid, have their own closed circular DNA and RNA, a complete protein synthesis apparatus (moreover, ribosomes of the prokaryotic type — 70S), multiply by binary fission, and thylakoid membranes are similar to prokaryotic membranes (the presence of acidic lipids ) and resemble the corresponding organelles in cyanobacteria.

glaucophyte algae, instead of typical chloroplasts, the cells contain cyanella — cyanobacteria that have lost the ability to live independently as a result of endosymbiosis, but partially retained the cyanobacterial cell wall [3] .

The age of this event is estimated at 1–1.5 billion years [4] .

Some groups of organisms received chloroplasts as a result of endosymbiosis not with prokaryotic cells, but with other eukaryotes that already have chloroplasts [5] . This explains the presence in the shell of the chloroplasts of some organisms more than two membranes [Ex. 2] . The innermost of these membranes is interpreted as a shell of a cyanobacterium that has lost its cell wall, while the outer one is interpreted as the wall of the host’s symbiontophore vacuole. Intermediate membranes — belong to a reduced eukaryotic organism that has entered into symbiosis. Some [Ex. 3] groups in the periplastid space between the second and third membranes there is a nucleomorph, a strongly reduced eukaryotic nucleus [6] .


In different groups of organisms, chloroplasts differ significantly in size, structure and number in the cell. Features of the structure of chloroplasts are of great taxonomic importance [7] . Basically, chloroplasts have the shape of a biconvex lens, their size is about 4-6 microns.

Chloroplast membrane

In different groups of organisms, the chloroplast membrane differs in structure.

Glaucocystophyte, red, green algae [8] and in higher plants, the shell consists of two membranes. In other eukaryotic algae, the chloroplast is additionally surrounded by one or two membranes. In algae with four-membrane chloroplasts, the outer membrane usually extends into the outer membrane of the nucleus.

Periplastid space

Lamella and thylakoids

Lamella connect thylakoid cavities


Pyrenoids are centers of polysaccharide synthesis in chloroplasts [9] . The structure of pyrenoids is diverse, and they are not always morphologically expressed. They can be intraplastid and stalked, protruding into the cytoplasm. In green algae and plants, pyrenoids are located inside the chloroplast, which is associated with the intraplastid storage of starch.


Stigmas or ocelli are found in the chloroplasts of motile algal cells. Located near the base of the flagellum. Stigmas contain carotenoids and are able to function as photoreceptors [10] .

See also

  • Photosynthesis
  • Triose Phosphate Translocator
  • Chromoplasts
  • Cyanella



  1. Chloroplasts of organisms belonging to the group of chromists have a four-layer membrane. It is assumed that in the history of their occurrence, the inclusion of one cell into another occurred twice.
  2. For example, dinophytes and euglenoids have 3 membranes, while ochrophytes have 4.
  3. In cryptophytes, chlorarachniophytes and some dinophytes.


  • Belyakova G. A. Algae and fungi // Botany: in 4 vols. «, 2006. — Vol. 1. — 320 p. — 3000 copies. — ISBN 5-7695-2731-5.
  • Karpov S.A. Protist cell structure. — St. Petersburg: TESSA, 2001. — 384 p. — 1000 copies. — ISBN 5-94086-010-9.
  • Lee, R.E. Physiology, 4th edition. — Cambridge: Cambridge University Press, 2008. — 547 p. — ISBN 9780521682770.

An excerpt describing Chloroplasts

– None. She lives where neither I nor you can go. Her earthly life here with us is over, and now she lives in another, very beautiful world, from which she can observe you. But she sees how you suffer, and she cannot leave here. And she can’t stay here any longer. That’s why she needs your help. Would you like to help her?
– How do you know all this? Why is she talking to you?!
I felt that as yet she did not believe me and did not want to recognize me as a friend. And I just couldn’t figure out how to explain to this little, ruffled, unfortunate girl that there is an “other”, distant world, from which, unfortunately, there is no return here. And that her beloved mother speaks to me not because she has a choice, but because I was just “lucky” to be a little “different” than everyone else …
“All people are different, Alynushka,” I began. — Some have a talent for drawing, others for singing, but I have such a special talent for talking with those who have left our world forever. And your mother speaks to me not at all because she likes me, but because I heard her when no one else could hear her. And I’m glad that I can help her in some way. She loves you very much and suffers very much because she had to leave … It hurts her very much to leave you, but this is not her choice. Do you remember, she was seriously ill for a long time? – girl nodded. “It was this sickness that made her leave you. And now she must go to her new world in which she will live. And for this, she must be sure that you know how much she loves you.
The girl looked at me sadly and asked quietly:
– Does she live with angels now?.. Dad told me that she now lives in a place where everything is like on postcards that I get for Christmas. And there are such beautiful winged angels… Why didn’t she take me with her?
The girl beamed.
– So I will see her there? she murmured happily.
— Of course, Alinushka. So you should just be a patient girl and help your mom now if you love her so much.
— What should I do? – the little girl asked very seriously.
— Just think of her and remember her because she sees you. And if you don’t be sad, your mom will finally find peace.
“Does she still see me?” the girl asked, and her lips began to twitch treacherously.
— Yes, honey.
She was silent for a moment, as if gathering herself inside, and then tightly clenched her fists and whispered softly:
– I will be very good, dear mommy . .. you go … go please … I love you so much! ..
Big peas of tears rolled down her pale cheeks, but her face was very serious and concentrated… For the first time life dealt her a cruel blow and it seemed as if this little, so deeply wounded, girl suddenly realized something for herself in an adult way and Now I tried to take it seriously and openly. My heart was breaking with pity for these two unfortunate and such sweet creatures, but, unfortunately, I could not help them anymore … The world around them was so incredibly bright and beautiful, but for both it could no longer be their common world …
Life is sometimes very cruel, and we never know what the meaning of the pain or loss that has been prepared for us is. Apparently, it is true that without losses it is impossible to comprehend what, by right or by a lucky chance, fate gives us. Only now, what could this unfortunate girl, cowering like a wounded animal, comprehend when the world suddenly collapsed on her with all its cruelty and the pain of the most terrible loss in life? . .
I sat with them for a long time and tried my best, help them both find some peace of mind. I remembered my grandfather and the terrible pain that his death brought me … How terrible it must have been for this fragile, unprotected baby to lose the most precious thing in the world — her mother? ..
We never think about the fact that those who, for one reason or another, are taken from us by fate, experience the consequences of their death much deeper than us. We feel the pain of loss and suffer (sometimes even angry) that they left us so ruthlessly. But what is it like for them when their suffering is multiplied a thousand times, seeing how we suffer from this?! And how helpless a person must feel, not being able to say anything more and change anything? ..
I would have given a lot then to find at least some opportunity to warn people about this. But, unfortunately, I did not have such an opportunity … Therefore, after the sad visit of Veronica, I began to look forward to when I could help someone else. And life, as it always usually happened, was not long in coming.
Entities came to me day and night, young and old, male and female, and everyone asked me to help them talk to their daughter, son, husband, wife, father, mother, sister … This continued in an endless stream, until, in the end, I I didn’t feel that I had no more strength. I didn’t know that when I came into contact with them, I had to be sure to close myself with my (and very strong!) Protection, and not open emotionally, like a waterfall, gradually giving them all my life force, which at that time, to Unfortunately, I didn’t know how to make up.
Very soon, I literally had no strength to move and fell into bed… When my mother invited our doctor, Dana, to check what had happened to me again, she said that it was my «temporary loss of strength from physical overwork»… I did not said nothing to anyone, although she knew perfectly well the real reason for this “overwork”. And as I did for a long time, I just honestly swallowed any medicine that my cousin prescribed me, and after lying in bed for about a week, I was again ready for my next “feats” . ..
I realized long ago that sincere attempts to explain what really happened to me gave me nothing but a headache and increased constant monitoring of me by my grandmother and mother. And in this, to be honest, I did not find any pleasure …

Source: o-ili-v.ru

Chloroplasts structure

Chloroplasts in algae, like in other plants, are surrounded by a membrane and consist of the main substance (stroma ) and lamellar or lamellar structures immersed in it, as well as various kinds of inclusions that differ in size, shape and composition of their contents (Fig. 6, 1i).[ …]

Chloroplasts have a certain autonomy in the cell system. They have their own ribosomes and a set of substances that determine the synthesis of a number of chloroplast’s own proteins. There are also enzymes, the work of which leads to the formation of lipids that make up the lamellae, and chlorophyll. As we have seen, the chloroplast also has an autonomous system for obtaining energy. Thanks to all this, chloroplasts are able to independently build their own structures. There is even a view that chloroplasts (like mitochondria) originated from some lower organisms that settled in a plant cell and first entered into symbiosis with it, and then became its integral part, an organoid.[ …]

Structure of chloroplasts.

The study of chloroplasts using an electron microscope showed that the membrane system here has a differentiated, very complex, but clearly ordered structure, which differs in different plants in the nature of the packaging and the degree of its severity. The membrane system is immersed in the stroma (or matrix) of the chloroplast, in which the enzymes associated with the reduction of carbon dioxide and the synthesis of carbohydrates are localized. An essential circumstance is that in chloroplasts, in addition to systems directly involved in the implementation of the photosynthesis process, there is also its own (other than nuclear) DNA, ribosomes and other components of protein-synthesizing systems. The chloroplasts of many algae are also characterized by the presence of a specific formation — a pyrenoid, the functional role of which remains unclear. Chloroplasts are capable of dividing and have an extremely diverse shape in different algae.[ …]

Diagram of the structure of the double lamella of the chloroplast

Light is usually required for the development of chloroplasts from proplastids. Development occurs by detaching flattened vesicles from the inner membrane, forming a flattened plate of thylakoids surrounded by a double membrane, in which chlorophyll is ultimately synthesized. Plastids that develop in this way are called etioplasts.[ …]

In the cytoplasm and chloroplasts of cells in the zone of chlorotic local necrosis caused by TMV and cucumber virus 4, groups of abnormal membrane-surrounded vesicles were found, and in chloroplasts, it is believed, they are formed as a result of protrusion of the membranes surrounding them. Cell spherosomes in the area around necrotic local lesions formed by TMVs on the leaves of N. glutinosa plants often contain single inclusions with a well-defined crystalline structure; such inclusions have not been found in normal cells [855].[ …]

Chlorophyll is formed under the light. Short thylakoids are stacked one above the other and form thylakoids grana. Plastids reach their final size (Fig. 30). Colorless plastids (leucoplasts—amploplasts) can also form directly from pro-plastids (Fig. 31). Leukoplasts are most often localized in cells of storage tissues. In many cases, in leucoplasts, the lamellae remain connected to the inner membrane. In the stroma of leukoplasts there are starch granules, osmiophilic globules, and protein inclusions. These globules are located in a continuous layer under the plastid membrane.[ …]

Light is required for the transformation of proplastids into chloroplasts. In the dark, the processes of synthesis and formation of membrane structures are interrupted. [ …]

It must be borne in mind that various structures found in an uninfected cell may resemble viral inclusions in their morphology. Thus, storage protein crystals and associated vesicles were found in young bean root chloroplasts [1267]; crystalline inclusions were found in chloroplasts of apparently healthy leaves of Masayatha [1360]. Marinos [1146] described plastids containing vacuoles and membranes in the meristem of the eyes of potato tubers. He called these formations “null-functional plastids”, but it is possible that some of the ultrastructures he discovered arose as a result of a “disguised” viral infection of the club.[ …]

Reservation (redundancy) of subcellular structures is an obvious thing. Structural redundancy is understood as the presence in the cell of functionally unambiguous elements in a larger quantity than is necessary for the normal operation of the system. This reduces the likelihood of system failure in the event of a very large load on its elements. An example is a large number of chloroplasts in a cell and their organization from a multitude of functionally equivalent thylakoids.[ …]

Chromoplasts arise either from proplastids, or from chloroplasts, or from leukoplasts. Their internal membrane structure is much simpler than that of chloroplasts. Gran no, the stroma contains a lot of yellow or orange pigment. Chromoplasts are contained in the cells of petals, fruits, root crops.[ …]

The microphotographs show (Figs. 10 and 11) how the structure of the thylakoid systems of leaves exposed to gassing changes. Thylakoids of chloroplasts of control plants in experiment 1 have the shape of oblong vesicles. Thylakoids in plants exposed to gassing, especially at an HC1 concentration of 0.25 mg/m3 of air, are characterized by the presence of regularly repeating electron-dense regions typical of fully developed chloroplasts. Thylakoids are more clearly united into grana, but due to the unequal diameter of the grana, their edges appear to be pointed. Probably, low concentrations of HC1 accelerate the formation of grains.[ …]

Chronic exposure to S02 causes other changes in the structure of chloroplasts: the stroma matrix becomes granular and agglomeration is observed. chloroplast as a biological structure that obeys the same laws of chemical signaling.[ …]

Bold and Solberg [67, 1640] using phase-contrast microscopy, discovered structures that they called «gray plates», which are formed at an early stage of crystal formation and which possibly consist of a single or double layer of oriented viral particles. Warmke and Edwardson (1865) described the process of crystal growth in tobacco leaf hair cells. At the first stages, in the cytoplasm of infected cells, viral particles were in a free state in the form of small aggregates of parallel rods connected at the ends. These aggregates then increase in size and form structures similar to Solberg and Bold’s «gray plates». In the process of growth, the crystals are not surrounded by any membrane, and, since they become multilayered, a part of the endoplasmic reticulum, mitochondria, and even chloroplast are sometimes included between their layers. [ …]

The luminescence is not caused by phosphorescence, but by the special structure of the lamellar structures of the protonema, sitting on upright branches growing in the direction of the light. The luminescent plate is directed against the incident light and is composed of lenticular cells with a convex anterior and funnel-shaped posterior wall. It is in the posterior corner of the cell that 4-6 chloroplasts are located. A beam of light is refracted by a spherical front wall, directed to the chloroplasts, passing through the chloroplast, reflected by the back wall; refracted again in the front wall, it emerges parallel to the input beam already as a green light. When the angle of incidence of light rays changes, the position of the chloroplasts also changes, gathering again in the focus of the refracted rays. By focusing light rays on chloroplasts, an optimal effect for photosynthesis is achieved under diffused light conditions.[ …]

Peroxide transformation of unsaturated fatty acids included in membrane structures is accompanied by impaired membrane semipermeability, loss of ability to plasmolysis, release of internal elements of cell organelles, osmotic imbalance, complete destruction of chloroplast granules. [ …]

This subdivision includes representatives with a unicellular thallus of a monadic structure (Fig. 61). The longitudinal groove is always worn along the ventral side, in the depression at the anterior end of the cell it passes into the triangular pharynx. Two unequal flagella emerge from the pharynx. Trichocysts (Fig. 61.1h, 3h) or mucous bodies (Fig. 61.4k) are located in the surface layer of the cytoplasm. Chloroplasts are numerous, small, discoid, light green, with oil drops between them. There are fewer pigments than in other groups, only chlorophyll a, -carotene and several xanthophylls were found. There are also colorless forms. The vacuum apparatus is complex. The core is large. Reserve substance — drops of fat. They are distributed mainly in sphagnum bogs, less often in lakes and other stagnant water bodies.[ …]

When a zoospore or zygote germinates, a siphon club-shaped structure is first formed, oriented vertically upwards. Before the formation of partitions begins in it, it reaches a noticeable size, differentiating into the basal (rhizoid) and apical parts. The chloroplast has a mesh structure (Fig. 236, 2), but, unlike the rest of the siphonoclads, in the cladophora the tendency to connect individual chloroplasts is more pronounced, so the chloroplast often looks like a solid, albeit perforated plate, and you can see that it consists from individual parts, is possible only with the help of special cytological techniques.[ …]

Plant cells are characterized by the presence of plastids. The most important plastids are chloroplasts. They convert light energy into chemical energy. Another important energy process (ATP synthesis due to oxidation energy) occurs in mitochondria. They are oval or rod-shaped structures 1–2 µm long. The system of tubules and cisterns (dictyosomes), bounded by a single-layer membrane, makes up the Golgi apparatus, the main function of which is the intracellular secretion of substances necessary for building the cell membrane, etc. Hydrolytic enzymes are concentrated in rounded bodies — lysosomes. Lipids are synthesized with the help of spherosomes. [ …]

The plasma membrane, the membrane of the endoplasmic reticulum, as well as nuclei, mitochondria and chloroplasts (see below) are extremely complex structures with a number of important biological properties. Many membranes contain enzymes, transport systems that carry out the transfer of nutrient molecules and inorganic ions into and within cells, as well as the removal of waste products from cells. Membrane structures are capable of self-healing if they are damaged for some reason.[ …]

In powdery mildew-affected plants, there is an increase in transpiration and a sharp deterioration in the structure of chloroplasts in the leaves. The crop shortage can reach 15% or more.[ …]

The main function of chloroblasts is the process of photosynthesis. In 1955, D. Ariope showed that the entire process of photosynthesis can be carried out in isolated chloroplasts. It is important to note that chloroplasts are not found only in leaf cells. The latter phenomenon (the chlorophylloposity of the embryo) attracts attention in plant systematics. Pokézalv research. that the structure of chloroplasts located in other organs of the plant, as well as the composition of pigments, are similar to leaf chlorolasts. This gives reason to believe that they are capable of photosynthesis. In the event that they are exposed to light, apparently, photosynthesis does occur in them. So, photosynthesis of chloroplasts. located in the awns of the ear, can be about 30% of the total photosynthesis of the plant. Roots turned green in the light are capable of photosynthesis. Photosynthesis can also take place in the chloroplasts that are in the skin of the fetus until a certain stage of its development. According to the assumption of A. L. Kursanov, chloroplasts located near the conductive pathways, releasing oxygen, contribute to an increase in the intensity of the metabolism of sieve tubes.[ …]

In the cells of algae, as well as in other green plants, but unlike fungal organisms, there is a chloroplast structure that provides the ability to photosynthesize. [ …]

as a result of the disorder in the structure of chloroplasts and the formation of various degradation products from chlorophyll, certain amounts of pheophytin accumulate in algae cells. Chlorophyll degradation products in toxicological experiments can make up a significant part of the total amount of green pigments, which leads to errors in the determination of chlorophyll, since they also absorb light in the red region of the spectrum. This fact must be taken into account.[ …]

Having reached a certain level, dysfunction of cells can be reflected in the next, higher level of organization. Changes in the structure of the lamellar system of chloroplasts, for example, as seen in electron microscopic photographs (Fig. 10 and I), can cause suppression of reduction reactions in the process of CO2 assimilation and retardation of growth and development, especially of leaves; damage at the cell level can be externally manifested in the form of chlorosis or necrosis.[ . ..]

T. Weier proposed a granular-lattice model, according to which the internal spaces of all tnlacoids are interconnected (Fig. 27). The chloroplasts of most algae have no granae, and the lamellae are collected in groups (packs) of 2–8 pieces. Not in all cases and in Fig. 27. Scheme of granular-mesh-higher plant chloroplasts Emeta chloroplast structure.[ …]

Subsequently, the development of the cell proceeded not along the line of improving this formation, but towards the creation of a qualitatively different, less bulky structure with similar functions, as evidenced by the absence of pyrenoids in plant chloroplasts, which occupy a higher stage of development compared to algae.[ .. .]

The basis of cell life is metabolism and energy conversion. The main source of energy on Earth is the Sun. Plant cells with special structures in chloroplasts capture the energy of the Sun, converting it into the energy of chemical bonds of molecules of organic substances and ATP. [ …]

Between the plasma membrane and the cell wall there is a connection in the form of desmoses — bridges. The cytoplasmic membrane often gives invaginations — invaginations into the cells. These invaginations form special membrane structures in the cytoplasm called mesosomes. Some types of mesosomes are bodies separated from the cytoplasm by their own membrane. Numerous vesicles and tubules are packed inside such membranous sacs (Fig. 2). These structures perform a variety of functions in bacteria. Some of these structures are analogues of mitochondria. By invagination of the cytoplasmic membrane, the photosynthetic apparatus of bacteria is also formed. After invagination of the cytoplasm, the membrane continues to grow and forms stacks (Table 30), which, by analogy with plant chloroplast granules, are called thylakoid stacks. Pigments (bacteriochlorophyll, carotenoids) and enzymes (cytochromes) that carry out the process of photosynthesis are localized in these membranes, which often fill most of the cytoplasm of a bacterial cell. [ …]

The emergence of the cell’s ability to divide in two or more planes led to the formation of a lamellar, sac-like and tubular structure of a very diverse shape (Table 31, 2, 6, 7). As in the Ulothrix, the thallus of the Ulviaceae is still poorly differentiated. Noticeably different from the rest are only large cells at the base of the plant, equipped with rhizoid processes, with the help of which the plants are attached. Just like in ulotrix, the cells of Ulvae contain a single parietal chloroplast with one or several pyrenoids and one nucleus located along the longitudinal axis of the cell.[ …]

The annual plant Poa annua (Poa annua) is one of the most sensitive to smog and its ubiquity makes it a very useful indicator of smog. Lesions are limited to those tapholes that are in the stage of maximum expansion. They appear at the top of the youngest leaves and gradually pass to older leaves. The initial and most severe lesion occurs in the environment of the substomatal chambers. The disintegration of chloroplasts is followed by plasmolysis and, finally, complete dehydration of the affected cells, which leads to the mummification of mesophilic tissue in the affected areas.[ …]

Bacteria: prokaryotes («pre-nuclear») unicellular organisms. Their cells do not have a nucleus separated from the cytoplasm. However, the genetic program, as in all living organisms, is encoded as a sequence of nucleotides in DNA and carries information about the structure of proteins. Bacterial cells do not contain organelles such as chloroplasts (specialized for photosynthesis) and mitochondria (specialized for cellular respiration and ATP synthesis). These biochemical processes occur in bacteria in the cytoplasm.[ …]

Live, non-fixed cells are also studied with a fluorescent microscope. Luminescence is the luminescence of an object as a result of the absorption of light energy, caused by ultraviolet, as well as blue and violet rays. Many cellular structures are capable of their own (primary) luminescence. Thus, chlorophyll contained in the chloroplasts of plant cells has a bright red luminescence; vitamins A and B, as well as some bacteria, have a fairly distinct glow.[ …]

A method has recently been proposed that can help identify virus particles in cells infected with 112181 small spherical viruses. Virus-like particles in Chenopodium plants, normally dispersed in the cytoplasm, have been found to form easily identifiable crystalline structures if leaves are allowed to tack slightly before fixing. . This observation reinforces the assumption that the formation of crystal structures in infected cells depends on the concentration of the virus. Using this technique, we did not observe large amounts of HPMT-like particles inside nuclei and chloroplasts. However, vesicular structures or bulges in the chlorolast membrane may contain HPMT-like particles. In withered leaf cells, many of these particles were also found in spaces between clustered chloroplasts (these spaces are roughly spherical in shape; Photo 58) (Ushiyama and Mathews, unpublished data). The material filling the spaces between chloroplasts included a large amount of labeled uridine [1036]. These experiments allowed us to arbitrarily conclude that the cytoplasm is the site of HPMT assembly in the cell. Regions of the cytoplasm between clustered chloroplasts may play some specific role as sites of HPMT synthesis and assembly; however, this conclusion requires confirmation.[ …]

Diatoms have been studied for almost 150 years, during this period more than one attempt was made to systematize them. All systems of diatoms can be divided into three groups, depending on what features they were based on: 1) the structure of cells and the type of colonies; 2) position, number and shape of chloroplasts; 3) the shape and detailed structure of the shell. The systems of the first two groups turned out to be unsuccessful, since the shape of the colonies and chloroplasts largely depends on environmental conditions and can often change. Even within the same genus, species have a different shape of chloroplasts and a different structure of colonies, depending on where they live — in plankton or benthos. And vice versa, genera that are not genetically related to each other, in the presence of external similarity in these characters, were included in the same systematic group. The systems of the third group are based on more permanent characters — on the structure of the shell and the details of its structure, which make it possible to establish family ties between taxa. In addition, such systems have one more advantage over the others: they can cover not only modern, but also fossil forms, and this is important when creating a truly phylogenetic system of diatoms.[ …]

If we consider the early stages of development of chalimeda and udothea (Fig. 229, 7-11), then the relationship of all siphon algae is striking. At first, the zygote grows, remaining mononuclear for some time. Then, at a later stage, it undergoes a series of cytological and morphological changes. One large nucleus divides, some chloroplasts lose their starch and turn into leucoplasts, the whole structure extends into a vertical siphon with a primary rhizoid at the base. The next stage has a multifilamentous structure. And only at the very latest stages of development does the interweaving and closing of vertical threads take place.[ …]

In the phase of heading and maturation, the content of manganese increases sharply in the ear. The same authors found that manganese is localized mainly in non-green cytoplasmic structures and large cell fragments. So, according to their data, large cell fragments of manganese contain 325.1 mg per 100 g of ash, or 16.3%; in chloroplasts 823.9, or 42.5%; in mitochondria 500, or 25.1%; in non-green cytoplasmic structures 321, or 16.1% manganese. T.A. Paribok (1959) believes that during the growing season there is more manganese in the leaves than in the stems. During the ripening period, it migrates to the ear, where its content increases to 38% of the total amount in plants. These data suggest that manganese is related mainly to the functioning, active organs of plants.[ …]

The staining pattern of these tubules suggests that they contain lipids or nucleic acids [1216]. Given the fact that they appear at very advanced stages of infection, it can be assumed that they are somehow related to the synthesis or assembly of the virus. However, we do not yet have any definite data on their role. Similar structures were also observed by other authors in cells infected with TMV. It has been suggested that these tubules are the direct precursors of the TMV rods; it is believed that rods could form from them as a result of processes of compaction and compression [1545]. The main objection against such a conclusion is currently put forward by the differences in the nature of staining of these tubules and TMV particles [1216], as well as the fact that such a stage is absent in the reconstruction of the TMV in vitro. It was not possible to observe TMV rods on thin sections of nuclei or chloroplasts in infected cells [1213, 1545]. However, chloroplasts in cells of diseased plants may form bulges or vacuolize, and TMV rods may be seen in such areas. Perhaps it is the existence of such invaginations that should explain the presence of small amounts of TMV in preparations of isolated chloroplasts. Localization of TMV in the cell may be different for different strains of the virus. Most of the work described above was performed on a typical TMV strain. However, for strain UR, for example, clear evidence of the presence of the virus in chloroplasts was obtained [1546]. Some of the contradictions in the literature may be due to differences in the behavior of different strains of the virus.[ …]

Surface membrane — plasma membrane isolates the cell from the environment. Cytoplasmic organelles have their own surface membranes. The vacuole is limited by the inner membrane of the cytoplasm — the tonoplast. Membranes also constitute the internal structure of such organelles as chloroplasts and mitochondria, increasing the surface on which the most important biochemical and biophysical processes take place.[ …]

disease, using a light microscope, you can easily detect a number of pathological abnormalities in the structure of chlorolasts. Islets of tissue in mosaic areas, having different shades of green, yellow and white, contained different strains of HPMT, each acting on the chloroplast in its own special and characteristic way (photo 37, color insert 1 and photo 56). [ …]

However, in the form in which they were applied, these systems did not make it possible to obtain any definite results. This is probably due to several reasons. First, in plant tissues, phenols are commonly present; they not only create difficulties in isolating viruses (chap. Secondly, nucleases are widespread in plant tissues, which quickly inactivate PIIK if they are removed or their activity is not suppressed. Thirdly, the presence of cellulose cell walls in plants means that rather harsh methods are required to destroy cells.Meanwhile, chloroplasts are fragile organelles, and therefore many preparations used as cell-free systems are contaminated with their fragments, which are very difficult to remove.Finally, fourthly, cells of adult, fully developed leaves have large vacuoles , the contents of which can damage cytoplasmic structures during cell destruction even before the protective substances present in the extracting medium play their role.[ …]

Fun Facts About Chloroplasts for Kids

If you have children of primary school age, their science classes will soon begin to focus on animal biology. plants, photosynthesis, and the fascinating and very important functions of chloroplasts.

So what are chloroplasts? A chloroplast is an organelle found in a plant cell.

The main function of chloroplasts is to promote photosynthesis by absorbing light energy. Another function of chloroplast organelles is to protect the plant from unwanted pathogens that can cause disease.

The chloroplast itself contains an important molecule called chlorophyll. Chlorophyll absorbs light energy from the sun and uses this energy to “synthesise” carbohydrates from carbon dioxide and water. This is how the plant generates the energy it needs to sustain life. This process (called photosynthesis) of removing carbon dioxide from the atmosphere and releasing oxygen is also necessary to sustain our life!

It rarely happens (unless, of course, you are a scientist, biologist, gardener or botanist!) that this kind of information is stored in adulthood. But don’t worry — we’ve put together a few key facts to help you help your kids with their science homework.

What do chloroplasts look like?

Image of © PUREPNG

Before we can get into our fun chloroplast facts, we need to know what a chloroplast looks like. This diagram shows a cross section of a chloroplast and what it is made of.

Outer membrane: The main protective shell of chloroplasts, the outer membrane is permeable, which means that small molecules can pass through it.

Inner diaphragm: Another layer of protection, the inner membrane, controls which molecules can enter and exit the structure.

Intermembrane Space: This is a tiny space between the inner and outer membranes, only 10 to 20 nanometers wide.

Stroma: This is a gel-like alkaline fluid that surrounds the thylakoids and other structures within the cell such as ribosomes, DNA and plastoglobuli.

Thylakoids: These are disc-shaped sacs containing chlorophyll arranged in a stack.

Lamella: These are bridge-like parts that help the thylakoids spread, this allows the chlorophyll to absorb as much light energy as possible.

Amazing Facts About Chloroplasts

1. The “chlorine” part of the word “chloroplast” comes from the Greek “chloros”, which means “green”.

2. All cells of green plants and algae contain chloroplasts, but they are absent in animal cells.

3. Scientists estimate that one square millimeter of an individual green leaf can contain about 500,000 chloroplasts.

4. Chloroplasts contain the following «ingredients»: proteins, chlorophyll, carbohydrates, carotenoids, ribosomes, lipids, DNA, RNA, enzymes and coenzymes. All of them are necessary for photosynthesis.

5. The outer membrane, inner membrane and intermembrane space are collectively referred to as the «chloroplast sheath».

6. Chloroplasts are able to wriggle inside their plant cell to find the best place to absorb sunlight.

7. Chloroplasts are sometimes called the «kitchen of the cell» because they are responsible for storing (and synthesizing) food.

8. The chloroplast stroma is also known as the «matrix». It is here that the synthesis of carbon dioxide, starch, sugar and fatty acids takes place. This process is controlled by many factors, including light, temperature, and even the length of the day, so it will be different in summer than it is in winter, for example.

9. If a plant is attacked by a pathogen, the chloroplasts will respond by producing enzymes that alert other plant cells of the invasion so they can help contain the attack.

10. Alternatively, chloroplasts can carry out a «supersensitive response». This is when chloroplasts initiate a process called «programmed cell death» or «PCD». This shuts down the system enough to kill any invading pathogens, sort of like a partial self-destruct mode, allowing other cells to start preparing defense molecules to kill the pathogen.

11. There are different opinions about who discovered this tiny structure and called it the chloroplast. Officially «opening» at 1905 is attributed to the Russian biologist Konstantin Mereshkovsky.

12. The scientific equation of photosynthesis looks like this:

6CO 2 + 6H 2O + light → C 6H 12O 6 + 6O 2

This translates as: carbon dioxide plus water produces carbohydrate plus oxygen. So the chloroplast can convert carbon dioxide and water into sugars and oxygen, smarty!

13. Have you ever wondered why chloroplasts are green? Green light actually damages chlorophyll and it cannot absorb it. This is why chloroplasts appear green as we humans see green light reflecting back towards us (all other colors of light are absorbed!)

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Do chloroplasts have DNA? 9 Facts You Should Know

This article illustrates all the information about «is there DNA in chloroplasts?» with 9 facts in detail

Chloroplast DNA, also known as plastid DNA, acts as a common semi-autonomous plant component that contains a helical circular double standard DNA molecule.

Now look at these 9 facts in a nutshell

  • Why do chloroplasts have DNA?
  • Where is DNA found in chloroplasts?
  • Do chloroplasts have circular DNA?
  • Chloroplast DNA structure
  • DNA of chloroplasts
  • DNA of chloroplasts
  • chloroplasts
  • 111111114







  • Difference between ChDNA and MitDNA

Why do chloroplasts have DNA?

Chloroplast DNA comes from endosymbionts, which are descended from cyanobacteria, also known as endosymbiotic cyanobacteria.

Chloroplast DNA, also known as plastid DNA, acts as a common semi-autonomous plant component. It has its own genetic systems with its own genome. It is a double helix, round double standard DNA molecule. The chloroplast is a type of bioenergetic subcellular organelle that has a double membrane, and it is a type of biconcave disc, 3 to 10 micrometers in diameter, consisting of a thylakoid that acts as a compartment containing flattened fluid-filled sacs.

The thylakoid arrangement appears as a stack, known as a granum (single thylakoid stack) or grana (plural of granum). An integral plate connects the grains to each other. Chloroplast DNA, also known as plastid DNA, acts as an abundant semi-autonomous plant component. It has its own genetic systems with its own genome. It is a double helical circular molecule of double standard DNA.

The cytosolic part contains a nuclear chromosomal gene encoding some precursor proteins and cytosolic proteins. After such import of genes into organelles in which it evolved as an endosymbiont. Simply aerobic prokaryotes are engulfed by eukaryotic cells, which enter into an endosymbiotic relationship or associate with a eukaryotic host to form their DNA.

Do chloroplasts have an example of DNA
Image from Wikimedia.org

Where is DNA found in chloroplasts?

The chloroplast has a double membrane structure with single DNA molecules present in multiple copies. The DNA of the chloroplast is enclosed in the stroma, the single fluid-filled interior of the chloroplast, and is attached to the chloroplast membrane.

It also has some other nuclear components, including RNA and ribosomes, starch granules, and some dissolved enzymes required for photosynthesis in a light-independent fashion , also known as the Calvin cycle.

Do chloroplasts have circular DNA?

Yes, the chloroplast has a circular double-stranded DNA that ranges from 120,000 to 247,000 nucleotides in length. The circular DNA of chloroplasts is genetically semi-autonomous.

They also contain several inverted repeats that have two tRNA genes and three ribosomal RNA genes. The inverted repeats of this chloroplast help to stabilize the entire chloroplast genome. There are several copies of about 100 nucleoids capable of storing identical ring chloroplasts.

Structure of chloroplast DNA

Chloroplast DNA, also known as plastid DNA, is a common component of total plant DNA. It is a double helical circular molecule of double standard DNA. In tall plants, the chloroplast can be 120 to 160 kb in size. and a length of 135,000 b.p.

Chloroplast DNA encodes certain structural proteins of the thylakoid membrane, chloroplast mRNA, rRNA and tRNA, and chloroplast ribosomal proteins that are essential for various chloroplast functions. For the light-dependent reaction and process of photosynthesis, the chloroplast membrane contains various kinds of enzymes, photosynthetic pigments, a single circular chromosome called DNA, and electronic careers.

Genes present in chloroplast DNA that code for a chloroplast apparatus for protein biosynthesis similar to the structural components of the chloroplast ribosome subunit, pol RNA subunit, and tRNA array. Chloroplast DNA contains the gene for the catalytically active subunit of the enzyme. RUBP-carboxylase , polypeptide components of the sunlight capture photosystem, rRNA gene , tRNA and ribosomal proteins , and contains units of chloroplast-specific RNA polymerase.

The gene of this chloroplast DNA determines the photosynthetic mechanism such as the electron transport chain, PS and PSI I. Photosynthetic pigments or one kind of chlorophyll molecules that are embedded in the thylakoid membrane and located in these two types of photosystem, PSI and PSII , Can absorb light and make the electron transport chain process for ATP synthesis. Most of the important properties of chloroplasts are inherited independently of nuclear genes, non-Mendelian, inheritance of somatic segregation in plants, and self-replication.

Function of chloroplast DNA

  1. Chloroplast DNA, also known as plastid DNA, encodes a gene for three electron transport proteins, nine photosystem II proteins, and three photosystem I proteins.
  2. The chloroplast gene is involved in photosynthesis in plants and other species activities.
  3. For the light-dependent reaction and photosynthesis process, a gene is used. Chloroplasts can produce various types of enzymes, and encode genes for photosynthetic pigments and electron careers.
  4. Chloroplast DNA encodes certain structural proteins of the thylakoid membrane, chloroplast mRNA, rRNA and tRNA, and chloroplast ribosomal proteins that are essential for various chloroplast functions.
  5. Chloroplast DNA inverted repeats help stabilize the entire genome of the chloroplast organelle.
  6. They can be inherited independently of nuclear genes, non-Mendelian inheritance of plant somatic segregation and self-reproduction.
  7. It encodes a total of 37 genes for tRNA molecules that carry out the translation process, 4 genes for the RNA polymerase subunit for transcription, and a total of 6 genes for the ATP synthase enzyme.
  8. It also contains genes for about 60 proteins to build a ribosome for their chloroplast

Chloroplast DNA replication

In the presence of light, DNA replication occurs independently during chloroplast division or cell cycle. It can also reproduce them in the dark through heterotrophic culture. Chloroplast DNA begins its replication unidirectionally using a single strategy known as the double bias loop or also known as the D-loop replication mechanism.

At the start of replication, several replication forks will start to open and this will allow the engine to begin the replication process. The movement of this D-loop takes an intermediate form of one theta, also known as an intermediate cairn replication, after which they complete their entire replication through a single mechanism known as the rolling circle mechanism. A new daughter chloroplast DNA chromosome is created when the chloroplast DNA structure is separated.

do chloroplasts have an example of DNA
Image from Wikipedia

Inheritance of chloroplast DNA

Inheritance of c. chloroplasts are commonly referred to as cytoplasmic heredity or extranuclear gene or extranuclear gene.

In cytoplasmic inheritance, gene transmission occurs outside the nucleus. There are two types of cytoplasmic DNA: mitochondrial DNA and chloroplast DNA. There are the most common examples of cytoplasmic inheritance, including inheritance in Oenothera, inheritance in mirabilis Jalapa and Zebrina.

Can chloroplasts reproduce?

Organelles are mainly dependent on their host. Chloroplasts do not reproduce, but chloroplasts can replicate their DNA during chloroplast proliferation.

The chloroplast has multiple copies of its genetic copies of the DNA molecule, also known as the plastome. The chloroplast can reproduce like bacteria by a process called binary fission, or by nuclear-encoded proteins.

Difference between ChDNA and MitDNA

The chloroplast DNA present inside plant cells is mainly responsible for the process of photosynthesis, while inside the eukaryotic cell there is mtDNA, which is mainly responsible for acting as the powerhouse of the cell. Human mitDNA has about 37 genes that code for polypeptide, rRNA, and tRNA, and mtDNA is about 16.569200 base pairs long. Chloroplast DNA contains about 120,000 genes containing between 120,000 and 170,000 base pairs.

chloroplast | Definition, function, structure, arrangement and scheme — Nauka

  • Nauka

Chloroplast , a structure within the cell of plants and green algae that is the site of photosynthesis, the process by which light energy is converted into chemical energy, resulting in the production of oxygen and energy-rich organic compounds. Photosynthetic cyanobacteria are free-living close relatives of chloroplasts; the endosymbiotic theory states that chloroplasts and mitochondria (energy-producing organelles in eukaryotic cells) originated from such organisms.

Chloroplast structure. The vesicles of the inner (thylakoid) membrane are organized into stacks, which are arranged in a matrix known as the stroma. All the chlorophyll in the chloroplast is contained in the membranes of the thylakoid vesicles. Encyclopædia Britannica, Inc.


What is a chloroplast?

Chloroplast is an organelle in the cells of plants and some algae that is the site of photosynthesis, which is the process by which energy from the sun is converted into chemical energy for growth. A chloroplast is a type of plastid (double-membrane sac-shaped organelle) that contains chlorophyll to absorb light energy.

Where are chloroplasts located?

Chloroplasts are present in the cells of all green tissues of plants and algae. Chloroplasts are also found in photosynthetic tissues that do not look green, such as the brown lobes of giant algae or the red leaves of some plants. In plants, chloroplasts are concentrated, in particular, in the parenchyma cells of the leaf mesophyll (the inner cell layers of the mesophyll). sheet).

Why are chloroplasts green?

Chloroplasts are green because they contain the pigment chlorophyll, which is vital for photosynthesis. Chlorophyll occurs in several different forms. Chlorophylls to and to are the main pigments of higher plants and green algae.

Is there DNA in chloroplasts?

Unlike most other organelles, chloroplasts and mitochondria have small round chromosomes known as extranuclear DNA. Chloroplast DNA contains genes that are associated with aspects of photosynthesis and other chloroplast activities. Both chloroplasts and mitochondria are believed to have evolved from free-living cyanobacteria, which may explain why they possess a PGA that is different from the rest of the cell.

Characteristics of chloroplasts

Learn about the structure of chloroplasts and their role in photosynthesis. Chloroplasts play a key role in the process of photosynthesis. Learn about the light reaction of photosynthesis in the grana and thylakoid membrane and the dark reaction in the stroma. Encyclopædia Britannica, Inc. Watch all videos for this article

Chloroplast is a type of plastid — a round, oval or disc-shaped body involved in the synthesis and storage of food. Chloroplasts are distinguished from other types of plastids by their green color, which is the result of the presence of two pigments: chlorophyll to and also chlorophyll b . These pigments are designed to absorb light energy during photosynthesis. Other pigments such as carotenoids are also present in chloroplasts and serve as additional pigments by capturing solar energy and transferring it to chlorophyll. In plants, chloroplasts are found in all green tissues, although they are concentrated especially in the mesophyll leaf parenchyma cells.

Dissect the chloroplast and identify its stroma, thylakoids, and chlorophyll-containing grana. Chloroplasts circulate in plant cells. The green color comes from the chlorophyll concentrated in the grana of the chloroplasts. Encyclopædia Britannica, Inc. Watch all videos for this article

Chloroplasts are approximately 1-2 µm thick (1 µm = 0.001 mm) and 5-7 µm in diameter. They are enclosed in a chloroplast membrane, which consists of a double membrane with an outer and inner layer, between which there is a gap called the intermembrane space. The third, inner membrane, highly folded and characterized by the presence of closed discs (or thylakoids), is known as the thylakoid membrane. In most higher plants, thylakoids are arranged in dense stacks called grana (single granulometry). The granules are connected by stromal plates, extensions that run from one granule through the stroma to the next. mustard . The thylakoid membrane surrounds a central watery area known as the thylakoid lumen. The space between the inner membrane and the thylakoid membrane is filled with stroma, a matrix containing dissolved enzymes, starch granules, and copies of the chloroplast genome.

Photosynthetic mechanism

The thylakoid membrane contains chlorophylls and various protein complexes, including photosystem I, photosystem II and ATP (adenosine triphosphate) synthase, which are specialized in light-dependent photosynthesis. When sunlight hits the thylakoids, the light energy excites the chlorophyll pigments, causing them to fail. electrons. The electrons then enter the electron transport chain, a series of reactions that ultimately lead to the phosphorylation of adenosine diphosphate (ADP) into energy-hungry stores. complex ATP. The electron transport also results in the formation of the reducing agent nicotinamide adenine dinucleotide phosphate (NADPH).

Chemiosmosis in chloroplasts Chemiosmosis in chloroplasts that results in proton transfer for the production of adenosine triphosphate (ATP) in plants. Encyclopædia Britannica, Inc.

ATP and NADPH are used in the light-independent reactions (dark reactions) of photosynthesis, in which carbon dioxide and water are assimilated into organic compounds. The light-independent reactions of photosynthesis are carried out in the chloroplast stroma, which contains the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Rubisco catalyzes the first step of carbon fixation in the Calvin cycle (also called the Calvin-Benson cycle), the main carbon transport pathway in plants. Among the so-called C 4 In plants, the initial stage of carbon fixation and the Calvin cycle are spatially separated — carbon fixation occurs through the carboxylation of phosphoenolpyruvate (PEP) in chloroplasts located in the mesophyll, while malate, the four-carbon product of this process, is transported to chloroplasts in a bundle. shell cells where the Calvin cycle takes place. C 4 photosynthesis tries to minimize the loss of carbon dioxide for photorespiration. In plants that use crassula acid metabolism (CAM), PEP carboxylation and the Calvin cycle are temporarily separated in chloroplasts, with the former occurring at night and the latter during the day. The CAM pathway allows plants to carry out photosynthesis with minimal water loss.

The chloroplast genome and membrane transport

The chloroplast genome is usually circular (although linear forms are also observed) and is approximately 120–200 kilobases in length. However, the modern chloroplast genome has significantly decreased in size: over time, evolution, an increase in the number of chloroplast genes were transferred to the genome in the cell nucleus. As a result, nuclear-encoded POGAGA ​​proteins have become important for chloroplast function. Therefore, the outer membrane of the chloroplast, which is freely permeable to small molecules, also contains transmembrane channels for the import of larger molecules, including nuclear-encoded proteins. The inner membrane is more restricted, with transport limited to certain proteins (eg, nuclear-encoded proteins) that are designed to pass through transmembrane channels.

Autotrophic nutrition. Photosynthesis Grade 10 online training at Rostelecom Lyceum

Subject: Fundamentals of Cytology

Lesson: Autotrophic nutrition. Photosynthesis


The sun has been and remains an inexhaustible source of energy for our planet. The most important aromorphosis of the Archean era was the emergence of photosynthesis, a process by which some living organisms learned to synthesize organic substances using sunlight as the main source of energy.

Photosynthesis is an extremely important process for the entire living population of our planet. It occurs in the cells of green plants, algae and in the cells of some bacteria, such as cyanobacteria, and is carried out with the help of various pigments, in particular, with the help of chlorophyll.


Chlorophyll in higher plants is concentrated in chloroplasts, and the main organ of photosynthesis in higher plants is the leaf. Chlorophyll has a special chemical structure that allows it to capture light quanta (Fig. 1).

Fig. 1. Absorption spectrum of chlorophyll

Chlorophyll absorbs mainly red and blue light. They reflect green light, and therefore give plants their characteristic green color, unless other pigments mask it. There are several forms of chlorophyll molecules, which differ in the wavelength of the captured light (Fig. 2).

Fig. 2. Spectrum of light absorbed by chlorophyll

Chlorophyll in higher plants is concentrated in chloroplasts, which determines their structure.


Structural and functional unit of chloroplasts are thylakoids – flat membranous sacs stacked in stacks (granas) (Fig. 3).

Fig. 3. The structure of the chloroplast

Individual grana are connected to each other by lamellae.

Thylakoid membranes contain special complexes, which include a chlorophyll molecule, as well as a molecule of electron carriers — cytochromes. The membrane system is where the light reactions of photosynthesis take place.

The structure of the chloroplast stroma resembles a gel – dark reactions take place here.

Excess carbohydrates formed during photosynthesis are stored in the form of starch grains.

Photosynthetic pigments

There are two types of photosynthetic pigments: primary and secondary. Pigments of the second type transfer the electrons they emit to the main pigment. The electrons emitted by the main pigment directly supply the energy for the photosynthesis reaction. The main catchers of light particles are two forms of chlorophyll a, which are designated as P700 and P680 (P is a pigment, 680 — 700 is the absorption maximum in nm). Other pigments play a supporting role.

It is now generally accepted that there are two photosynthetic units, which are called photosystem 1 and photosystem 2. Each of these units consists of a set of auxiliary pigments that transfer energy to the main pigment molecule, namely to the molecule of chlorophyll a (Fig. 4 ).

Fig. 4. The structure of the photosystem and the antenna complex of light-gathering pigments

This molecule is called a reaction center. In a reaction center, energy is used to carry out a chemical reaction.

Fig. 5. Transfer of electrons to the reaction center

It is here that the conversion of light energy into the energy of chemical bonds occurs, which is the central event of photosynthesis (Fig. 5).

Phases of Photosynthesis

Photosynthesis occurs in two phases, namely the light phase and the dark phase.

During the light phase, energy is generated, which is then spent on dark reactions. The process of the light phase of photosynthesis includes non-cyclic photophosphorylation and photolysis of water. Oxygen is released as a by-product of the reaction as a result of the photolysis of water. The reaction occurs on the thylakoid membranes.

A red light quantum absorbed by chlorophyll P680 (photosystem II) transforms an electron into an excited state (Fig. 6). An electron excited by light acquires a large supply of energy, as a result of which it moves to a higher energy level. Such an electron is captured by the electron acceptor X, moving from one stage to another, that is, from one acceptor to another, it loses energy, which is used for the synthesis of ATP.

Fig. 6. Scheme of the processes of the light phase of photosynthesis

The place of the released electrons of the P680 chlorophyll molecule is occupied by the electrons of water, since water undergoes photolysis under the action of light, where oxygen is formed as a by-product. Photolysis occurs in the cavity of the thylakoid (Fig. 7).

Fig. 7. Photolysis of water

In photosystem I, excited electrons under the action of a photon of light also move to a higher level and are captured by the acceptor Y. Eventually, the electrons reach the carrier — NADP, and, interacting with hydrogen ions released during the photolysis of water , form reduced NADPH. NADP stands for nicotinamide adenine dinucleotide phosphate.

Fig. Fig. 8. Interaction of photosystem I and photosystem II

The place of released electrons in the P700 molecule is occupied by electrons received from photosystem II P680 (Fig. 8). Thus, in the light, electrons move from water to photosystems II and I, and then to NADP. This unidirectional flow of electrons is called non-cyclic electron flow, and the formation of ATP that occurs is called non-cyclic photophosphorylation. Thus, energy-rich ATP and reduced NADP are formed in the light phase, and oxygen is released as a by-product of the reaction.

Dark phase of photosynthesis . If the light phase proceeds only in the light, then the dark phase does not depend on the light. The dark phase takes place in the chloroplast stroma, where energy-rich compounds, namely ATP and reduced NADP, are transferred, in addition, carbon dioxide enters there as a source of carbohydrates, which is taken from the air and enters the plants through the stomata. In dark phase reactions, carbon dioxide is reduced to glucose using the energy stored by ATP and NADP molecules.

The conversion of carbon dioxide into glucose during the dark phase of photosynthesis is called the Calvin cycle, after its discoverer.

The first stage of photosynthesis — light — occurs on the chloroplast membranes in the thylakoids.

The second stage of photosynthesis — dark — takes place inside the chloroplast, in the stroma.

The overall photosynthesis equation is as follows. When 6 molecules of carbon dioxide and 6 molecules of water interact, one molecule of glucose is formed and six molecules of oxygen are released. This process takes place in the light in the chloroplasts of higher plants.

Thus, photosynthesis is a process of transformation of matter and energy.

Importance of photosynthesis

As a result of photosynthesis, plants accumulate organic matter and ensure the constancy of carbon dioxide and oxygen in the atmosphere. In the upper layers of the air shell, ozone is formed from oxygen, which has the chemical formula O 3 . The ozone shield protects all life on our planet from the penetration of dangerous short-wave ultraviolet rays.

K. A. Timiryazev (Fig. 9) said: “There is hardly any process taking place on the surface of the Earth that deserves such a degree of general attention as that far from unraveled process that occurs in a green leaf when a a ray of the sun. Considered from a chemical point of view, this is the process in which inorganic matter, carbon dioxide and water, is converted into organic matter. Viewed from a physical, dynamic point of view, this is the process in which the living force of a solar ray is converted into chemical stress, into a supply of work. Viewed from both points of view, this is a process on which, in the final instance, all manifestations of life on our planet depend.

Fig. 9. Portrait of K.A. Timiryazev

Chloroplast pigments

All photosynthetic organisms contain pigments that are able to capture sunlight, namely the visible part of the solar spectrum, thereby triggering photosynthesis reactions. From photosynthetic organisms, in particular from plants, pigments are extracted using various solvents such as alcohol and acetone. The separation of the pigments is then carried out using chromatography. For the first time, this was done on a sorbent column by the Russian scientist M. S. Tsvet at 1903 — he used chalk and powdered sugar as a sorbent (Fig. 10).

Fig. 10. Adsorption column proposed by M.S. Tsvet (On the photo)

MS Tsvet invented a fundamentally new method for separating pigments and isolated the following pigments: chlorophyll a, chlorophyll b and several fractions of yellow pigments (Fig. 11).

Fig. 11. Chromatogram of chlorophylls a and b

The method of adsorption chromatography is now widely used in scientific practice for the separation of substances.

Plant organisms contain several types of pigments that perform specific functions. As a rule, plastids of higher plants and algae contain three classes of basic pigments — chlorophylls, carotenoids and phycobilins. Chlorophylls and carotenoids are generally insoluble in water, while phycobilins are soluble.

Table 1.

Distribution of pigments in photosynthetic eukaryotic organisms.

Chlorophyll a is found in all photosynthetic organisms presented in Table 1, because it is the main pigment of photosynthesis.

Carotenoids as auxiliary pigments are also found in all photosynthetic organisms presented in Table 1, while phycobilins are found only in red algae.

The presence of pigments is also associated with the spread of photosynthetic organisms deep into the oceans (Fig. 13). For example, green algae are common up to 30 m, as they absorb red light more actively.

Fig. 13. Absorption of sunlight by living organisms in the oceans

Phycobilins (Fig. 14) absorb light in the yellow-green regions of the spectrum.

Fig. 14. Absorption of sunlight by phycobilin

This feature allows red algae (Fig. 15) living in the depths of the sea to carry out photosynthesis using a weak bluish green light that penetrates through the water column.

Fig. 15. Red algae

In addition, red algae contain phycoerythrin, or red phycobilin. It gives red algae their characteristic color.

Semi-autonomous chloroplasts

Chloroplasts, like mitochondria, are semi-autonomous structures. They contain a circular DNA molecule, ribosomes and various forms of RNA, that is, their own protein-synthesizing system. This allows them to partially provide themselves with protein. The circular DNA molecule is also characteristic of bacteria.

Eukaryotes are characterized by linear DNA. Ribosomes in chloroplasts are the same as in bacteria, belonging to the 70S type. That is, chloroplasts are more like bacteria that have lost their independence. Of great interest is the question of the origin of chloroplasts in the process of evolution. Chloroplasts, regardless of the nucleus, are capable of division, differentiation and synthesis of their own proteins. However, they are still partially dependent on the nucleus due to the fact that not all the proteins necessary for life can synthesize themselves.

It is believed that chloroplasts used to be free-living cyanobacteria (Fig. 16) that were engulfed by a heterotrophic cell.

Fig. 16. Cyanobacteria — photosynthetic prokaryotes

But for some reason, she did not digest cyanobacteria, but began to use them as symbionts. Over time, these free-living cyanobacteria, which entered into symbiosis with a heterotrophic cell, lost their independence and began to reside inside this cell in the form of organelles. This event led to the emergence of photosynthetic organisms.

For example, isolated mammalian cells can capture chloroplasts by phagocytosis, while chloroplasts in mammalian cells retain their structure and viability for 6 cell divisions. And chloroplasts isolated from mammalian cells are capable of photosynthesis.

Emerson enhancement effect

The idea of ​​the existence of two photosynthetic systems in plants was first proposed by Robert Emerson (Fig. 17), studying the dependence of the efficiency of photosynthesis on the wavelength of light.

Fig. 17. Robert Emerson

In the unicellular alga Chlorella (Fig. 18), he analyzed the effect of light wavelength on the quantum yield of photosynthesis, that is, the amount of oxygen released during photosynthesis per 1 quantum of absorbed energy.

Fig. 18. Single-celled alga Chlorella

Emerson found that chlorella was most effective for photosynthesis in red light with a wavelength of 650 to 680 nm, and blue light with a wavelength of 400 to — 460 nm. It is this light that is absorbed by chlorophyll. He also calculated that the photosynthetic efficiency of red light was 36% higher than that of blue light.

In the following experiments, it was shown that if the cells were illuminated with red light with a wavelength of 650 to 680 nm, the quantum yield was quite high.

However, with a further increase in the wavelength of light above 685 nm, the quantum yield of photosynthesis fell sharply.

If chlorella is illuminated with both short-wave (650 nm) and long-wave (700 nm) red light, the total effect will be greater than with each beam separately. This phenomenon was called the Emerson amplification effect, and led Emerson to suggest that there are two photosynthetic systems in plants that must work in concert.

Thus, photosynthesis is the process of formation of organic matter from carbon dioxide and water in the light with the participation of photosynthetic pigments (chlorophyll in plants, bacteriochlorophyll and bacteriorhodopsin in bacteria). This is the most important stepwise energy process — the basis for the existence of the modern biosphere.


1. What organisms are called autotrophs?

2. What organisms are able to feed autotrophically through photosynthesis?

3. What is a photosystem? Why do plants have two photosystems?

4. Where do the reactions of the light phase of photosynthesis take place? What happens to water during photosynthesis?

5. What happens during the dark phase? What is a set of dark reactions called?


By alexxlab

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