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==Structure==
==Structure==


Chloroplasts are observable as flat discs usually 2 to 10 micrometers in diameter and 1 micrometer thick. In land plants, they are, in general, 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.
Chloroplasts are the mother fucking shizznets. dammm nighaaa observable as flat discs usually 2 to 10 micrometers in diameter and 1 micrometer thick. In land plants, they are, in general, 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.


[[Image:Chloroplast.svg|thumb|275px|right|Chloroplast ultrastructure:<br />
[[Image:Chloroplast.svg|thumb|275px|right|Chloroplast ultrastructure:<br />

Revision as of 01:52, 11 November 2009


The simplified internal structure of a chloroplast

Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. 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.[1]

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 plastids.

Evolutionary origin

Chloroplasts visible in thefruited Thyme-moss

eggs smell good!!!!!!!!!!!!!!!!!!=)

A model chloroplast

Chloroplasts are one of the many different types of organelles in the cell. In general, they are considered to have originated as endosymbiotic cyanobacteria (previously known as blue-green algae). This was first suggested by Mereschkowsky in 1905 [2] after an observation by Schimper in 1883 that chloroplasts closely resemble cyanobacteria. [3] 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.Cite error: A <ref> tag is missing the closing </ref> (see the help page).

Structure

Chloroplasts are the mother fucking shizznets. dammm nighaaa observable as flat discs usually 2 to 10 micrometers in diameter and 1 micrometer thick. In land plants, they are, in general, 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.

Chloroplast ultrastructure:
1. outer membrane
2. intermembrane space
3. inner membrane (1+2+3: envelope)
4. stroma (aqueous fluid)
5. thylakoid lumen (inside of thylakoid)
6. thylakoid membrane
7. granum (stack of thylakoids)
8. thylakoid (lamella)
9. starch
10. ribosome
11. plastidial DNA
12. plastoglobule (drop of lipids)

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 ribosomes; however most of its proteins are encoded by genes contained in the host cell nucleus, with the protein products transported to the chloroplast.

TEM image of a chloroplast

Within the stroma are stacks of thylakoids, the sub-organelles, which are the site of photosynthesis. The thylakoids are arranged in stacks called grana (singular: granum).[4] 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 electron microscope, thylakoid membranes appear as alternating light-and-dark bands, each 0.01 μm thick. Embedded in the thylakoid membrane are antenna complexes, each of which consists of the light-absorbing pigments, including chlorophyll and carotenoids, as well as proteins that bind the pigments. 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.

Recent studies have shown that chloroplasts can be interconnected by tubular bridges called stromules, formed as extensions of their outer membranes.[5][6] Chloroplasts appear to be able to exchange proteins via stromules,[7] and thus function as a network.

Transplastomic plants

Recently, chloroplasts have caught attention by developers of genetically modified plants. In most flowering plants, chloroplasts are not inherited from the male parent,[8][9] although in plants such as pines, chloroplasts are inherited from males.[10] Where chloroplasts are inherited only from the female, transgenes 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 coexistence of conventional and organic agriculture. While the reliability of this mechanism has not yet been studied for all relevant crop species, recent results in tobacco plants are promising, showing a failed containment rate of transplastomic plants at 3 in 1,000,000.[9]

See also

Notes

  • Public Domain This article incorporates public domain material from Science Primer. NCBI. Archived from the original on 2009-12-08.

References

  1. ^ Campbell, Neil A. (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  2. ^ Mereschkowsky C (1905). "Über Natur und Ursprung der Chromatophoren im Pflanzenreiche". Biol Centralbl. 25: 593–604.
  3. ^ Schimper AFW (1883). "Über die Entwicklung der Chlorophyllkörner und Farbkörper". Bot. Zeitung. 41: 105–14, 121–31, 137–46, 153–62.
  4. ^ Campbell, Neil A. (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Köhler RH, Hanson MR (2000). "Plastid tubules of higher plants are tissue-specific and developmentally regulated". J. Cell. Sci. 113 (Pt 1): 81–9. PMID 10591627. {{cite journal}}: Unknown parameter |day= ignored (help); Unknown parameter |month= ignored (help)
  6. ^ Gray JC, Sullivan JA, Hibberd JM, Hansen MR (2001). "Stromules: mobile protrusions and interconnections between plastids". Plant Biology. 3: 223–33. doi:10.1055/s-2001-15204.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Köhler RH, Cao J, Zipfel WR, Webb WW, Hanson MR (1997). "Exchange of protein molecules through connections between higher plant plastids". Science (journal). 276 (5321): 2039–42. PMID 9197266. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  8. ^ Stegemann S, Hartmann S, Ruf S, Bock R (2003). "High-frequency gene transfer from the chloroplast genome to the nucleus". Proc. Natl. Acad. Sci. U.S.A. 100 (15): 8828–33. doi:10.1073/pnas.1430924100. PMC 166398. PMID 12817081. most angiosperm species inherit their chloroplasts maternally {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  9. ^ a b Ruf S, Karcher D, Bock R (2007). "Determining the transgene containment level provided by chloroplast transformation". Proc. Natl. Acad. Sci. U.S.A. 104 (17): 6998–7002. doi:10.1073/pnas.0700008104. PMC 1849964. PMID 17420459. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
  10. ^ Powell W, Morgante M, McDevitt R, Vendramin GG, Rafalski JA (1995). "Polymorphic simple sequence repeat regions in chloroplast genomes: applications to the population genetics of pines". Proc. Natl. Acad. Sci. U.S.A. 92 (17): 7759–63. doi:10.1073/pnas.92.17.7759. PMC 41225. PMID 7644491. In the pines, the chloroplast genome is transmitted through pollen {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
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