Difference between revisions of "Chloroplast" - New World Encyclopedia
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| − | '''Chloroplasts''' are | + | '''Chloroplasts''' are organelles (compartments) found in [[plant]] (cell (biology)|cell]] and [[eukaryote|eukaryotic]] [[alga]]e that conduct [[photosynthesis]]. |
| + | |||
| + | Utilizing [[chlorophyll]] and water, chloroplasts capture [[light]] [[energy]] from the [[sun]] to produce the free [[energy]] stored in [[Adenosine triphosphate|ATP]] and NADPH through a process called [[photosynthesis]]. The photosynthetic process also produced food for the organism in the form of [[sugar]]. In the process, carbon dioxide is consumed and oxygen is released. The overall process can be depicted as. | ||
| + | |||
| + | :6 CO<sub>2</sub> + 12 H<sub>2</sub>O + light → C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> + 6 O<sub>2</sub> + 6 H<sub>2</sub>O | ||
| + | |||
| + | :Carbon Dioxide + Water + Light energy → Glucose + Oxygen + Water | ||
| + | |||
| + | The term chloroplast is derived from the Greek words ''chloros'' which means "green" and ''plast'' which means "form" ( in biological terms, it can be more roughly translated as organelle or cell ). | ||
==Origins== | ==Origins== | ||
| − | Chloroplasts | + | Chloroplasts are generally considered to have originated as [[symbiosis|endosymbiotic]] [[cyanobacteria]], as theory known as the endosymbiotic theory. In this respect they are similar to [[mitochondrion|mitochondria]], but are found only in [[plant]]s and [[protist]]a. Both organelles are surrounded by a double celled composite membrane with an intermembrane space; both have their own [[DNA]] and are involved in energy [[metabolism]]; and both have reticulations, or many infoldings, filling their inner spaces. |
| − | In green plants chloroplasts are surrounded by two [[cell membrane|lipid-bilayer membrane]]s. The inner membrane is now thought to correspond to the outer membrane of the ancestral cyanobacterium. The chloroplast genome is considerably [[genome reduction|reduced]] compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities. Many of the missing genes are encoded in the nuclear genome of the host. | + | In green plants, chloroplasts are surrounded by two [[cell membrane|lipid-bilayer membrane]]s. The inner membrane is now thought to correspond to the outer membrane of the ancestral cyanobacterium. The chloroplast genome is considerably [[genome reduction|reduced]] compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities. Many of the missing genes are encoded in the nuclear genome of the host. |
It is interesting to note that in some algae (such as the [[heterokont]]s and other [[protist]]s such as [[Euglenozoa]] and [[Cercozoa]]), chloroplasts seem to have arisen 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 have themselves been engulfed by still other eukaryotes, forming tertiary endosymbionts. | It is interesting to note that in some algae (such as the [[heterokont]]s and other [[protist]]s such as [[Euglenozoa]] and [[Cercozoa]]), chloroplasts seem to have arisen 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 have themselves been engulfed by still other eukaryotes, forming tertiary endosymbionts. | ||
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Chloroplasts are flat discs usually 2-10 micrometer in diameter and 1 micrometer thick. The chloroplast has a two membrane envelope termed the Inner & Outer membrane respectively. Between these two layers is the Intermembrane space. | Chloroplasts are flat discs usually 2-10 micrometer in diameter and 1 micrometer thick. The chloroplast has a two membrane envelope termed the Inner & Outer membrane respectively. Between these two layers is the Intermembrane space. | ||
| − | The fluid within the chloroplast is called the [[stroma]], corresponding to the [[cytoplasm]] of the bacterium, and contains tiny circular DNA and [[ribosome]]s, though most of their proteins are encoded by genes contained in the cell nucleus, with the protein products | + | The fluid within the chloroplast is called the [[stroma]], corresponding to the [[cytoplasm]] of the bacterium, and contains tiny circular DNA and [[ribosome]]s, though most of their proteins are encoded by genes contained in the cell nucleus, with the protein products transported to the |
| + | chloroplast. | ||
| − | Within the stroma are stacks of [[thylakoid]]s, the sub-organelles where photosynthesis actually takes place. A stack of thylakoids is called a [[granum]]. A thylakoid looks like a flattened disk, and inside is an empty area called the thylakoid space or lumen. The photosynthesis reaction takes place on the membrane of the thylakoid, and, as is also the case with mitochondria, involves the coupling of cross-membrane [[flux]]es with [[biochemistry|biosynthesis]]. | + | Within the stroma are stacks of [[thylakoid]]s, the sub-organelles where photosynthesis actually takes place. A stack of thylakoids is called a [[granum]] (plural: grana). A thylakoid looks like a flattened disk, and inside is an empty area called the thylakoid space or lumen. The photosynthesis reaction takes place on the membrane of the thylakoid, and, as is also the case with mitochondria, involves the coupling of cross-membrane [[flux]]es with [[biochemistry|biosynthesis]]. |
| + | |||
| + | Embedded in the thylakoid membrane is a dish of chlorophyll molecules known as an antenna complex, this outer array helps to increase the surface area of light capture. The light photons are then funneled to the centre of this complex. Two chlorophyll molecules are then ionised, producing an excited electron which then passes onto the photochemical reaction centre. | ||
==See also== | ==See also== | ||
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:*[[Outer membrane]] | :*[[Outer membrane]] | ||
*[[Calvin cycle]] | *[[Calvin cycle]] | ||
| + | |||
==References== | ==References== | ||
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*[http://reference.allrefer.com/encyclopedia/C/chloropl.html Chloroplast, Botany] | *[http://reference.allrefer.com/encyclopedia/C/chloropl.html Chloroplast, Botany] | ||
*[http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=8041699 Use of chloroplast DNA in studying plant phylogeny and evolution] | *[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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| − | {{credit| | + | {{credit|84197481}} |
[[Category:Life sciences]] | [[Category:Life sciences]] | ||
Revision as of 01:57, 8 November 2006
Chloroplasts are organelles (compartments) found in plant (cell (biology)|cell]] and eukaryotic algae that conduct photosynthesis.
Utilizing chlorophyll and water, chloroplasts capture light energy from the sun to produce the free energy stored in ATP and NADPH through a process called photosynthesis. The photosynthetic process also produced food for the organism in the form of sugar. In the process, carbon dioxide is consumed and oxygen is released. The overall process can be depicted as.
- 6 CO2 + 12 H2O + light → C6H12O6 + 6 O2 + 6 H2O
- Carbon Dioxide + Water + Light energy → Glucose + Oxygen + Water
The term chloroplast is derived from the Greek words chloros which means "green" and plast which means "form" ( in biological terms, it can be more roughly translated as organelle or cell ).
Origins
Chloroplasts are generally considered to have originated as endosymbiotic cyanobacteria, as theory known as the endosymbiotic theory. In this respect they are similar to mitochondria, but are found only in plants and protista. Both organelles are surrounded by a double celled composite membrane with an intermembrane space; both have their own DNA and are involved in energy metabolism; and both have reticulations, or many infoldings, filling their inner spaces.
In green plants, chloroplasts are surrounded by two lipid-bilayer membranes. The inner membrane is now thought to correspond to the outer membrane of the ancestral cyanobacterium. The chloroplast genome is considerably reduced compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities. Many of the missing genes are encoded in the nuclear genome of the host.
It is interesting to note that in some algae (such as the heterokonts and other protists such as Euglenozoa and Cercozoa), chloroplasts seem to have arisen 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 endosymbionts have themselves been engulfed by still other eukaryotes, forming tertiary endosymbionts.
Structure
Chloroplasts are flat discs usually 2-10 micrometer in diameter and 1 micrometer thick. The chloroplast has a two membrane envelope termed the Inner & Outer membrane respectively. Between these two layers is the Intermembrane space.
The fluid within the chloroplast is called the stroma, corresponding to the cytoplasm of the bacterium, and contains tiny circular DNA and ribosomes, though most of their proteins are encoded by genes contained in the cell nucleus, with the protein products transported to the chloroplast.
Within the stroma are stacks of thylakoids, the sub-organelles where photosynthesis actually takes place. A stack of thylakoids is called a granum (plural: grana). A thylakoid looks like a flattened disk, and inside is an empty area called the thylakoid space or lumen. The photosynthesis reaction takes place on the membrane of the thylakoid, and, as is also the case with mitochondria, involves the coupling of cross-membrane fluxes with biosynthesis.
Embedded in the thylakoid membrane is a dish of chlorophyll molecules known as an antenna complex, this outer array helps to increase the surface area of light capture. The light photons are then funneled to the centre of this complex. Two chlorophyll molecules are then ionised, producing an excited electron which then passes onto the photochemical reaction centre.
See also
- Chloroplast membrane
- Inner membrane
- Outer membrane
ReferencesISBN links support NWE through referral fees
- This article contains material from the Science Primer published by the NCBI, which, as a US government publication, is in the public domain at http://www.ncbi.nlm.nih.gov/About/disclaimer.html.
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
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