Structure and function of chloroplast pdf
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- Editorial: Structure and Function of Chloroplasts
- Structure and function of the chloroplast signal recognition particle
- Chloroplast evolution, structure and functions
Editorial: Structure and Function of Chloroplasts
Essentially, chloroplasts are plastids found in cells of higher plants plants with advanced traits with lignified tissue for transport of water and minerals and algae as sites of photosynthesis. This makes them the most important cell organelles given that plants are the primary producers and the base of all food chains. Depending on the type of plant or algae, the number of chloroplasts in a cell may range from 1 to They are located in the cell cytoplasm and move across the cell cytoplasm along with the cellular fluids.
These organelles serve as sites of manufacture and storage either or both functions and include chromoplasts chloroplast is a type of chromoplast and leucoplasts such as elaioplast and amyloplast.
Compared to other organelles like the mitochondria, chloroplasts are relatively larger ranging from 4 to 10 micrometers in diameter and about 2 micrometers in thickness.
While they may appear spherical or ovoid in maize plant, they are seen to appear as spiral coils in spirogya. However, the shape of a mature chloroplast is always regular. However, DNA is also found in organelles classified as plastids including mitochondria and chloroplast. Compared to other organelles, chloroplasts have three types of membranes that serve different functions.
These include:. Outer envelope membrane OEM - Being the outer most membrane, the outer envelope membrane OEM plays an important role as the physical barrier between the organelle and the cytoplasmic environment.
Communication between the inner components of the organelle and the cytoplasmic environment is mediated by this membrane. Some of the primary functions of the OEM include the importation of proteins nuclear-encoded proteins movement diffusion of other compounds with low molecular weight and ions, as well as such functions as the site for biosynthesis of lipids.
One of the most important properties of the outer membrane is that it contains high amount of lipids than protein ratio. This characteristic makes the OEM the lightest membrane of the three.
These channels serve to regulate the movement of molecules and ions in and out of the chloroplast. Inner envelope membrane - Compared to the outer membrane that is usually considered to be a more passive barrier, the inner envelope membrane IEM is more selective and only allows some compounds and metabolites in and out of the organelle.
For the most part, transport across the inner membrane is regulated by active transport where the proteins located in the membrane IEM actively transport molecules and ions.
These transporters have been shown to perform their function more effectively when they are hydrophobic repelling water or not mixing with water. Through active transport of metabolites and other ions etc, the inner membrane ensures that there is equilibrium of raw material anabolic precursors and the final products from the organelle.
Some of the other functions of the inner envelope membrane include the synthesis of different types of metabolites and cell division of the organelle. Because the inner membrane is highly folded with roughly the same protein lipid ratio, it is heavier compared to the outer envelope membrane.
Thylakoid membrane system - This system makes up the internal membrane system. This system appears as flattened disks and is the site of photosynthesis on the membrane the thylakoid membrane enclose thylakoid that are arranged in stacks 10 to 20 stacks known as grana. Here, these stacks are all connected by a single membrane with the stroma thylakoids stroma lamellae connecting the grana.
The architecture of thylakoid varies from one plant to another. As a result, there are three different models of thylakoid including:.
Like the other membranes, the thylakoid system is made up of lipid bi-layers galactosyl diglyceride is an example of lipids making up the membrane system with most of the lipids being those found in other plastid membranes galactosyl diglycerides etc. The thylakoid membrane also encloses the thylakoid lumen, which is a single, large aqueous space. All these different parts of the thylakoid system play an important role in photosynthesis. The stroma and grana are the two main parts of the thylakoid.
As such, they are also composed of different types and composition of proteins. See more on Chlorophyll. Basically, photosynthesis is the process through which plants and other primary producers are able to convert energy from sunlight to chemical energy that is in turn used to convert water, carbon-dioxide and minerals into organic compounds glucose. In the thylakoid system, this takes place on the thylakoid membrane and stroma.
Here, the photosynthetic pigments are embedded in the thylakoid membrane. The process photosynthesis involves two major stages including the light phase light reactions and the dark phase dark reactions.
These photosystems contain chlorophyll pigments that absorb light energy. When sunlight is absorbed by the peripheral chlorophyll molecules in photosystem II , it is transported through Resonance Energy Transfer RET to the reaction center, which is the central pair of chlorophyll molecules. In the process, the energy causes the electrons to be exited at a higher state and the subsequent loss of electrons from the photosystem.
Since they contain chlorophyll pigment that absorbs sunlight energy they release electrons that are then transported through the electron transfer chain. Plastoquinone PQ - Before the electrons arrive at the cytochrome bf complex, they have to be carried by carriers to this destination.
This role is carried out by plastoquinone. When the electrons are released from the photosystems PSII , they are accepted by plastoquinone it also accepts hydrogen ions from the stroma. Electrons from the photosystems are then transported by plastoquinone to the cytochrome b6f complex while the hydrogen ions protons are transported to the lumen thylakoid lumen which is also important or synthesis and production of ATP. Cytochrome b6f complex - Electrons carried by plastoquinone are transported to the cytochrome bf complex, which in turn transfers these electrons as well as protons from stroma to the plastocyanin.
During photosynthesis, this complex enzyme and contributes in the transfer of electrons to PSI while mediating in the pumping of protons into thylakoid lumen space to contribute in the synthesis of ATP.
Plastocyanin PC - From the cytochrome bf complex, electrons are transferred to the plastocyanin, which acts as a carrier that in turn transports these electrons to PSI. As with PSII, photons cause the electrons to become exited and act at higher energy level.
Ferredoxin acts as a carrier that accepts the electrons and consequently reduced to give up the electrons for synthesis of NADPH. Here, the protons Hydrogen ion transported in the electron transfer chain provides the energy required to produce ATP from the phospholylation of ADP adenosine di-phosphate. The light reaction involves two important steps which include photolysis and photophosphorylation. Whereas photolysis is the process involved in water splitting releasing oxygen, hydrogen and electrons photophosphorylation uses these components to produce ATP energy, which is a chemical energy.
However, it can also occur through another process known as cyclic-photophosphorylation cyclic electron flow where the end product is only ATP. Unlike light dependent reactions, light-independent reactions take place in the stroma of the chloroplast which is filled with fluids. As the name suggests, dark reactions do not require light energy and thus take place in the absence of light as such, they are also refered to as light independent reactions. By using the Calvin Cycle, it becomes easier to understand the light independent reaction:.
This process takes place in the absence of light in the dark it starts with the plant taking in carbon-dioxide through the stomata pores on the surface of leaves which moves to the stroma. The processes that follow are divided into three main phases. This reaction results in the production of a compound with six carbon that is then converted into two 3-Phosphoglyceric acid, a compound with three carbons.
To view chloroplasts under the microscope, students can use toluidine blue stain to prepare a wet mount. This simply involves the following simple steps:.
Observation - When viewed under the microscope, students will be able to distinguish different parts of the cell including the plastids chloroplast and mitochondria. On the other hand, a simply wet mount even without staining will show chloroplast to be small green or dark green sports across the cell surface.
Return to page on Plastids. Return to Plant Biology overview. Return to learning about Algae. Return to Cell Biology.
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Structure and function of the chloroplast signal recognition particle
The targeting of proteins, including the insertion and translocation of proteins in or across membranes, is a fundamental process within a cell, and a variety of specialized mechanisms for protein transport have been developed during evolution. The signal recognition particle SRP is found in the cytoplasm of most, if not all, eukaryotes and prokaryotes where it plays a central role in the co-translational insertion of membrane proteins into the endoplasmic reticulum and plasma membrane, respectively. Interestingly, chloroplasts contain a specialized type of signal recognition particle. A mechanism of protein transport that has been extensively studied is the co-translational protein transport to the endoplasmic reticulum ER of eukaryotic cells. The cytosolic components, as well as the membrane components like the receptors and the translocation pore, have been characterized reviewed in Martoglio and Dobberstein ; Rapoport et al.
Chloroplasts are plant cell organelles that convert light energy into relatively stable chemical energy via the photosynthetic process. By doing so, they sustain life on Earth. Chloroplasts also provide diverse metabolic activities for plant cells, including the synthesis of fatty acids, membrane lipids, Chloroplasts also provide diverse metabolic activities for plant cells, including the synthesis of fatty acids, membrane lipids, isoprenoids, tetrapyrroles, starch, and hormones. The biogenesis, morphogenesis, protection and senescence of chloroplasts are essential for maintaining a proper structure and function of chloroplasts, which will be the theme of this Research Topic. Chloroplasts are enclosed by an envelope of two membranes which encompass a third complex membrane system, the thylakoids, including grana and lamellae.
Chloroplasts carry out a number of other functions, including fatty acid synthesis , much amino acid synthesis, and the immune response in plants. The number of chloroplasts per cell varies from one, in unicellular algae, up to in plants like Arabidopsis and wheat. A chloroplast is a type of organelle known as a plastid , characterized by its two membranes and a high concentration of chlorophyll. Other plastid types, such as the leucoplast and the chromoplast , contain little chlorophyll and do not carry out photosynthesis. Chloroplasts are highly dynamic—they circulate and are moved around within plant cells, and occasionally pinch in two to reproduce. Their behavior is strongly influenced by environmental factors like light color and intensity. Chloroplasts, like mitochondria , contain their own DNA , which is thought to be inherited from their ancestor—a photosynthetic cyanobacterium that was engulfed by an early eukaryotic cell.
Address correspondence to zoschke mpimp-golm. Chloroplast translation is essential for cellular viability and plant development. Its positioning at the intersection of organellar RNA and protein metabolism makes it a unique point for the regulation of gene expression in response to internal and external cues. Recently obtained high-resolution structures of plastid ribosomes, the development of approaches allowing genome-wide analyses of chloroplast translation i. In this review, we provide an overview of the current knowledge of the chloroplast translation machinery, its structure, organization, and function.
Gene expression in chloroplasts is controlled primarily through the regulation of translation. This regulation allows coordinate expression between the plastid and nuclear genomes, and is responsive to environmental conditions. Despite common ancestry with bacterial translation, chloroplast translation is more complex and involves positive regulatory mRNA elements and a host of requisite protein translation factors that do not have counterparts in bacteria.
In this review, we consider a selection of recent advances in chloroplast biology. These include new findings concerning chloroplast evolution, such as the identification of Chlamydiae as a third partner in primary endosymbiosis, a second instance of primary endosymbiosis represented by the chromatophores found in amoebae of the genus Paulinella , and a new explanation for the longevity of captured chloroplasts kleptoplasts in sacoglossan sea slugs. Other topics covered in this review include new protein components of nucleoids, an updated inventory of the chloroplast proteome, new enzymes in chlorophyll biosynthesis and new candidate messengers in retrograde signaling. Finally, we discuss the first successful synthetic biology approaches that resulted in chloroplasts in which electrons from the photosynthetic light reactions are fed to enzymes derived from secondary metabolism.
Essentially, chloroplasts are plastids found in cells of higher plants plants with advanced traits with lignified tissue for transport of water and minerals and algae as sites of photosynthesis.
Chloroplast evolution, structure and functions
The primary energy resource of life on earth is the sun, whose energy is captured in the form of usable carbons by a process called photosynthesis. Photosynthesis occurs within a cellular organelle adapted to that purpose, called the chloroplast. Chloroplasts are unique metabolic and sensory organelles restricted to plants, algae, and a few protists.
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. Chloroplasts are present in the cells of all green tissues of plants and algae.
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PDF | In this review, we consider a selection of recent advances in chloroplast biology. These include new findings concerning chloroplast.