Plant cells with visible chloroplasts.

Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed Plant cells are eukaryotic cells that differ in several key respects from the cells of other eukaryotic Organisms Their distinctive features Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Algae ( sing. alga are a large and diverse group of simple typically Autotrophic organisms ranging from Unicellular to Multicellular forms Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. Chloroplasts absorb light and use it in conjunction with water and carbon dioxide to produce sugars, the raw material for energy and biomass production in all green plants and the animals that depend on them, directly or indirectly, for food. Biomass, in Ecology, is the mass of living biological organisms in a given area or Ecosystem at a given time Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In Thermodynamics, the term thermodynamic free energy refers to the amount of work that can be extracted from a System, and is helpful in Engineering Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy Nicotinamide adenine dinucleotide phosphate ( NADP+, in older notation triphosphopyridine nucleotide TPN) is used in anabolic reactions such as Lipid Nicotinamide adenine dinucleotide phosphate ( NADP+, in older notation triphosphopyridine nucleotide TPN) is used in anabolic reactions such as Lipid It is derived from the Greek words chloros which means green and plast which means form or entity. Chloroplasts are members of a class of organelles known as plastids. Plastids are major Organelles found in plants and algae Plastids often contain pigments used in photosynthesis and the types of pigments present can change

Evolutionary origin

Chloroplasts are one of the many unique organelles in the plant cell. They are generally considered to have originated as endosymbiotic cyanobacteria (i. The endosymbiotic theory concerns the origins of mitochondria and Plastids (e Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of Bacteria that obtain their energy e. blue-green algae). This was first suggested by Mereschkowsky in 1905 ^[1] after an observation by Schimper in 1883 that chloroplasts closely resemble cyanobacteria. ^[2] All eukaryote chloroplasts are thought to derive directly or indirectly from a single endosymbiotic event (in the Archaeplastida), except for Paulinella chromatophora, which has recently acquired a photosynthetic cyanobacterial endosymbiont which is not closely related to chloroplasts of other eukaryotes. The Archaeplastida or Primoplantae are a major line of Eukaryotes comprising the land plants green and Red algae and a small Paulinella is a genus of about nine species of freshwater Amoeboids Its most famous member is the photosynthetic P ^[3] In that they derive from an endosymbiotic event, chloroplasts are similar to mitochondria but chloroplasts are found only in plants and protista. In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. Plants are living Organisms belonging to the kingdom Plantae. Protists (ˈproʊtɨst are a diverse group of eukaryotic Microorganisms Historically protists were treated as the kingdom Protista but this The chloroplast is surrounded by a double-layered composite membrane with an intermembrane space; it has its own DNA and is involved in energy metabolism. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known Further, it has reticulations, or many infoldings, filling the inner spaces.

In green plants, chloroplasts are surrounded by two lipid-bilayer membranes. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer The inner membrane is now believed to correspond to the outer membrane of the ancestral cyanobacterium. Chloroplasts have their own genome, which is considerably reduced compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities with the cyanobacterial genome. Genome size refers to the total amount of DNA contained within one copy of a Genome. Plastids may contain 60-100 genes whereas cyanobacteria often contain more than 1500 genes. ^[4] Many of the missing genes are encoded in the nuclear genome of the host. The transfer of nuclear information has been estimated in tobacco plants at one gene for every 16000 pollen grains. Tobacco is an Agricultural product recognized as an addictive drug processed from the fresh Leaves of plants in the genus Nicotiana. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance ^[5]

In some algae (such as the heterokonts and other protists such as Euglenozoa and Cercozoa), chloroplasts seem to have evolved through a secondary event of endosymbiosis, in which a eukaryotic cell engulfed a second eukaryotic cell containing chloroplasts, forming chloroplasts with three or four membrane layers. The heterokonts or stramenopiles are a major line of Eukaryotes presently containing about 10500 known species The Euglenozoa are a large group of Flagellate protozoa They include a variety of common free-living species as well as a few important parasites some of which infect humans The Cercozoa are a group of Protists including most Amoeboids and Flagellates that feed by means of filose pseudopods In some cases, such secondary endosymbionts may have themselves been engulfed by still other eukaryotes, thus forming tertiary endosymbionts. An endosymbiont is any Organism that lives within the body or cells of another organism i

Structure

The internal structure of a chloroplast, with a granal stack of thylakoids circled.

Chloroplasts are observable morphologically as flat discs usually 2 to 10 micrometer in diameter and 1 micrometer thick. The chloroplast is contained by an envelope that consists of an inner and an outer phospholipid membrane. Between these two layers is the intermembrane space.

The material within the chloroplast is called the stroma, corresponding to the cytosol of the original bacterium, and contains one or more molecules of small circular DNA. The cytosol or intracellular fluid (or cytoplasmic matrix) is the liquid found inside cells. It also contains ribosomes, although most of its proteins are encoded by genes contained in the host cell nucleus, with the protein products transported to the chloroplast. Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that

Within the stroma are stacks of thylakoids, the sub-organelles which are the site of photosynthesis. A Thylakoid is a membrane-bound compartment inside Chloroplasts and cyanobacteria. The thylakoids are arranged in stacks called grana (singular: granum). A thylakoid has a flattened disk shape. Inside it is an empty area called the thylakoid space or lumen. Photosynthesis takes place on the thylakoid membrane; as in mitochondrial oxidative phosphorylation, it involves the coupling of cross-membrane fluxes with biosynthesis via the dissipation of a proton electrochemical gradient. In the various subfields of Physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as

Embedded in the thylakoid membrane is the antenna complex, which consists of proteins, and light-absorbing pigments, including chlorophyll and carotenoids. Chlorophyll is a green Pigment found in most Plants Algae and Cyanobacteria. Carotenoids are organic Pigments that are naturally occurring in Chromoplasts of plants and some other photosynthetic Organisms This complex both increases the surface area for light capture, and allows capture of photons with a wider range of wavelengths. The energy of the incident photons is absorbed by the pigments and funneled to the reaction centre of this complex through resonance energy transfer. Förster resonance energy transfer (abbreviated FRET) also known as Fluoresence resonance energy transfer or resonance energy transfer ( RET Two chlorophyll molecules are then ionised, producing an excited electron which then passes onto the photochemical reaction centre.

Transplastomic plants

Recently, chloroplasts have caught attention by developers of genetically modified plants. Genetically modified plants are genetically engineered to contain one or more Genes of another species In certain plant species, such as tobacco, chloroplasts are not inherited from the male, and therefore, transgenes in these plastids cannot be disseminated by pollen. A transgene is a Gene or genetic material that has been transferred by any of a number of Genetic engineering techniques from one organism to another Pollen is a fine to coarse powder consisting of microgametophytes ( pollen grains) which produce the male Gametes (sperm cells of This makes plastid transformation a valuable tool for the creation and cultivation of genetically modified plants that are biologically contained, thus posing significantly lower environmental risks. Plastid transformation is a method in the Genetic engineering of plants This biological containment strategy is therefore suitable for establishing the coexistence of conventional and organic agriculture. Biological containment (or biocontainment describes measures aimed at preventing Genetically modified organisms (GMOs and their Transgenes from spreading into the In the context of agriculture and food and feed production co-existence means using cropping systems with and without Genetically modified organisms (GMOs in parallel The reliability of this mechanism has not yet been studied for all relevant crop species. However, the research programme Co-Extra recently published results for tobacco plants, demonstrating that the containment of transplastomic plants is highly reliable with a tiny failure rate of 3 in 1,000,000. Co-Extra is an EU-funded research programme on ''co-ex''istence and ''tra''ceability of genetically modified crops and their edible derivatives ^[6]

See also

• Chloroplast membrane

• Inner membrane
• Outer membrane

• Calvin cycle
• Light-dependent reaction

References

• This article contains material from the Science Primer published by the NCBI, which, as a U. Chloroplasts contain several important membranes vital for their function The inner membrane is the Biological membrane (phospholipid bilayer of an Organelle or Gram-negative Bacteria that is within an Outer The outer membrane refers to the outside membranes of Gram-negative bacteria, the Chloroplast, or the Mitochondria. The Calvin cycle (or Calvin-Benson-Bassham cycle or carbon fixation is a series of biochemical reactions that takes place in the Stroma of Chloroplasts The initial stage of the photosynthetic system is the light-dependent reaction, which converts solar energy into Potential energy. The National Center for Biotechnology Information ( NCBI) is part of the United States National Library of Medicine (NLM a branch of the National Institutes S. government publication, is in the public domain. The public domain is a range of abstract materials &ndash commonly referred to as Intellectual property &ndash which are not owned or controlled by anyone

External links

• Chloroplasts and Photosynthesis: The Role of Light from Kimball's Biology Pages
• Chloroplast, Botany
• Use of chloroplast DNA in studying plant phylogeny and evolution
• 3D structures of proteins associated with thylakoid membrane
• Co-Extra research on chloroplast transformation