Chloroplast: Difference between revisions
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[[Image:Chloroplast-new.jpg|thumb|300px|right|The inside of a chloroplast]] |
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'''Chloroplasts''' are [[organelle]]s found in [[plant cell]]s and [[eukaryote|eukaryotic]] [[alga]]e that conduct [[photosynthesis]]. Chloroplasts absorb light and use it in conjunction with water and carbon dioxide to produce sugars, the raw material for energy and [[Biomass (ecology)|biomass]] production in all green plants and the animals that depend on them, directly or indirectly, for food. Chloroplasts capture [[light]] [[energy]] to conserve [[Thermodynamic free energy|free energy]] in the form of [[Adenosine triphosphate|ATP]] and reduce [[NADP]] to [[NADPH]] through a complex set of processes called photosynthesis. The word chloroplast 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 [[plastid]]s. |
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==Evolutionary origin== |
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[[Image:Chloroplasten.jpg|thumb|right|250px|Plant cells with visible chloroplasts.]] |
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Chloroplasts are one of the many different types of organelles in the cell. They are generally considered to have originated as [[endosymbiotic theory|endosymbiotic]] [[cyanobacteria]] (i.e. blue-green algae). This was first suggested by [[Konstantin Mereschkowski|Mereschkowsky]] in 1905 <ref>{{cite journal | author= Mereschkowsky C | title= Über Natur und Ursprung der Chromatophoren im Pflanzenreiche | journal= Biol Centralbl | year=1905 | volume=25 | pages=593–604}} </ref> after an observation by Schimper in 1883 that chloroplasts closely resemble cyanobacteria. <ref>{{cite journal | author= Schimper AFW | title= Über die Entwicklung der Chlorophyllkörner und Farbkörper | journal= Bot. Zeitung | year=1883 | volume=41 | pages=105–14, 121–31, 137–46, 153–62}} </ref> All 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.<ref>{{cite journal | title = Diversity and evolutionary history of plastids and their hosts | author = Patrick J. Keeling | url = http://www.amjbot.org/cgi/content/full/91/10/1481 | journal = American Journal of Botany | year = 2004 | volume = 91 | pages = 1481–1493 | doi = 10.3732/ajb.91.10.1481}}</ref> In that they derive from an endosymbiotic event, chloroplasts are similar to [[mitochondrion|mitochondria]] but chloroplasts are found only in [[plant]]s and [[protist]]a. 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. Further, it has reticulations, or many infoldings, filling the inner spaces. |
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In green plants, chloroplasts are surrounded by two [[cell membrane|lipid-bilayer membrane]]s. The inner membrane is now believed to correspond to the outer membrane of the ancestral cyanobacterium. Chloroplasts have their own genome, which is considerably [[genome reduction|reduced]] compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities with the cyanobacterial genome. Plastids may contain 60-100 genes whereas cyanobacteria often contain more than 1500 genes.<ref>{{ cite journal | author= Martin W, Rujan T, Richly E, Hansen A, Cornelson S, Lins T, Leister D, Stoebe B, Hasegawa M, Penny D | title= Evolutionary analysis of Arabidopsis, cyanobacterial, and chloroplast genomes reveals plastid phylogeny and thousands of cyanobacterial genes in the nucleus | journal = Proc Natl Acad Sci | year = 2002 | volume=99 | pages=12246–12251 | doi= 10.1073/pnas.182432999 | pmid= 12218172}}</ref> 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.<ref>{{cite journal | author=Huang CY, Ayliffe MA, Timmis JN | title=Direct measurement of the transfer rate of chloroplast DNA into the nucleus | journal=Nature | date =2003-03-06 | volume=422 | issue=6927 | pages=72–6 | doi=10.1038/nature01435}}</ref> |
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In some algae (such as the [[heterokont]]s 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. In some cases, such secondary [[endosymbiont]]s may have themselves been engulfed by still other eukaryotes, thus forming tertiary endosymbionts. In the alga ''Chlorella'', there is only one chloroplast, which is bell shaped. |
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In some groups of [[mixotrophic]] [[protist]]s such as the [[dinoflagellate]]s, chloroplasts are separated from a captured alga or diatom and used temporarily. These [[kleptoplasty|klepto chloroplasts]] may only have a lifetime of a few days and are then replaced.<ref name=Skovgaard>Skovgaard, A (1998) Role of chloroplast retention in a marine dinoflagellate. ''Aquatic Microbial Ecology'' 15, 293-301</ref> |
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==Structure== |
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Chloroplasts are observable morphologically as flat discs usually 2 to 10 micrometer in diameter and 1 micrometer thick. In land plants they are generally 5 μm in diameter and 2.3 μm 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. A typical [parenchyma] cell contains about 10 to 100 chloroplasts. |
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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. It also contains [[ribosome]]s, although most of its proteins are encoded by genes contained in the host cell nucleus, with the protein products transported to the chloroplast. |
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[[Image:Chloroplast.svg|thumb|275px|right|Chloroplast ultrastructure:<br /> |
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1. outer membrane<br /> |
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2. intermembrane space<br /> |
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3. inner membrane (1+2+3: envelope)<br /> |
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4. stroma (aqueous fluid)<br /> |
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5. thylakoid lumen (inside of thylakoid)<br /> |
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6. thylakoid membrane<br /> |
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7. granum (stack of thylakoids)<br /> |
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8. thylakoid (lamella)<br /> |
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9. starch<br /> |
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10. ribosome<br /> |
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11. plastidial DNA<br /> |
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12. plastoglobule (drop of lipids) |
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]] |
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Within the stroma are stacks of [[thylakoid]]s, the sub-organelles which are the site of photosynthesis. 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 [[flux]]es with [[biochemistry|biosynthesis]] via the dissipation of a proton electrochemical gradient. |
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In the electron microscope, thylakoid membranes appear as alternating light-and-dark bands, each 0.01 μm thick. Embedded in the thylakoid membrane is the antenna complex, which consists of the light-absorbing pigments, including [[chlorophyll]] and [[carotenoids]], and proteins (which bind the chlorophyll). 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]]. Two chlorophyll molecules are then ionised, producing an excited electron which then passes onto the photochemical reaction centre. |
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Recent studies have shown that chloroplasts can be interconnected by tubular bridges called [[stromule]]s, formed as extensions of their outer membranes.<ref name=Köhler2000>Köhler RH & Hanson MR (2000) Plastid tubules of higher plants are tissue-specific and developmentally regulated. Journal of Cell Science 113, 81–89</ref><ref name=Gray2001>Gray JC, Sullivan JA, Hibberd JM & Hansen MR (2001) Stromules: mobile protrusions and interconnections between plastids. Plant Biology 3, 223–233</ref> Chloroplasts appear to be able to exchange proteins via stromules,<ref name=Köhler1997>Köhler RH, Cao J, Zipfel WR, Webb WW & Hanson MR (1997) Exchange of protein molecules through connections between higher plant plastids. Science 276, 1039–1042</ref> and thus function as a network. |
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==Transplastomic plants== |
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Recently, chloroplasts have caught attention by developers of [[genetically modified plant]]s. In most flowering plants, chloroplasts are not inherited from the male parent,<ref>{{cite journal | quote = most angiosperm species inherit their chloroplasts maternally | doi = 10.1073/pnas.1430924100 | pmc = 166398 | year = 2003 | month = July | author = Stegemann, S; Hartmann, S; Ruf, S; Bock, R | title = High-frequency gene transfer from the chloroplast genome to the nucleus | volume = 100 | issue = 15 | pages = 8828–33 | pmid = 12817081 | journal = Proceedings of the National Academy of Sciences of the United States of America | url = http://www.pnas.org/cgi/pmidlookup?view=long&pmid=12817081 | format = Free full text }}</ref><ref name="ruf2007"/> although in plants such as pines, chloroplasts are inherited from males.<ref>{{cite journal | pmc = 41225 | quote = In the pines, the chloroplast genome is transmitted through pollen | journal = Proc Natl Acad Sci U S A. | date = 1995-08-15 | volume = 92 | issue = 17 | pages = 7759–7763 | doi = 10.1073/pnas.92.17.7759 | title = Polymorphic Simple Sequence Repeat Regions in Chloroplast Genomes: Applications to the Population Genetics of Pines | author = Powell, W. | pmid = 7644491 }}</ref> Where chloroplasts are inherited only from the female, [[transgene]]s in these plastids cannot be disseminated by [[pollen]]. 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. This [[biological containment]] strategy is therefore suitable for establishing the [[Co-existence of genetically modified and conventional crops and derived food and feed|coexistence of conventional and organic agriculture]]. 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.<ref name="ruf2007">{{cite journal | author=Ruf S, Karcher D, Bock R | title=Determining the transgene containment level provided by chloroplast transformation | journal=PNAS | date=2007-04-24 | volume=104 | issue=17 | pages=6998–7002 | doi=10.1073/pnas.0700008104 | pmid=17420459 | pmc = 1849964 }}</ref> |
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==See also== |
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*[[Chloroplast membrane]] |
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:*[[Inner membrane]] |
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:*[[Outer membrane]] |
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*[[Calvin cycle]] |
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*[[Light-dependent reaction]] |
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==Notes==<!-- MolPhylogenetEvol48:23,48:176,48:313 --> |
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<div class="references-small" style="-moz-column-count:2; column-count:2;"> |
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<references /></div> |
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==References== |
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*{{NCBI-scienceprimer}} |
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==External links== |
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*[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Chloroplasts.html Chloroplasts] and [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/L/LightReactions.html Photosynthesis: The Role of Light] from [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/ Kimball's Biology Pages] |
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*[http://reference.allrefer.com/encyclopedia/C/chloropl.html Chloroplast, Botany] |
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*[http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=8041699 Use of chloroplast DNA in studying plant phylogeny and evolution] |
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*[http://opm.phar.umich.edu/localization.php?localization=Thylakoid%20membrane 3D structures of proteins associated with thylakoid membrane] |
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*[http://www.coextra.eu/projects/project199.html Co-Extra research on chloroplast transformation] |
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{{organelles}} |
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{{Botany}} |
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[[Category:Organelles]] |
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[[Category:Photosynthesis]] |
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[[ar:صانعات يخضورية]] |
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[[bn:ক্লোরোপ্লাস্ট]] |
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[[bg:Хлоропласт]] |
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[[ca:Cloroplast]] |
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[[cs:Chloroplast]] |
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[[da:Grønkorn]] |
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[[de:Chloroplast]] |
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[[et:Kloroplast]] |
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[[el:Χλωροπλάστης]] |
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[[es:Cloroplasto]] |
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[[eo:Kloroplasto]] |
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[[fa:سبزدیسه]] |
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[[fr:Chloroplaste]] |
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[[gl:Cloroplasto]] |
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[[ko:엽록체]] |
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[[hr:Kloroplast]] |
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[[id:Kloroplas]] |
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[[is:Grænukorn]] |
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[[it:Cloroplasto]] |
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[[he:כלורופלסט]] |
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[[lt:Chloroplastas]] |
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[[hu:Kloroplasztisz]] |
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[[mk:Хлоропласт]] |
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[[ms:Kloroplas]] |
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[[nl:Bladgroenkorrel]] |
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[[ja:葉緑体]] |
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[[no:Kloroplast]] |
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[[nn:Kloroplast]] |
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[[oc:Cloroplast]] |
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[[nds:Chloroplast]] |
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[[pl:Chloroplast]] |
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[[pt:Cloroplasto]] |
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[[ro:Cloroplast]] |
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[[ru:Хлоропласт]] |
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[[simple:Chloroplast]] |
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[[sk:Chloroplast]] |
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[[sl:Kloroplast]] |
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[[sr:Хлоропласт]] |
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[[sh:Hloroplast]] |
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[[su:Kloroplas]] |
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[[fi:Viherhiukkanen]] |
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[[sv:Kloroplast]] |
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[[th:คลอโรพลาสต์]] |
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[[vi:Lục lạp]] |
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[[tr:Kloroplast]] |
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[[uk:Хлоропласт]] |
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[[zh:叶绿体]] |
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Revision as of 20:06, 19 November 2008
jacob sucks