Chloroplast

Chloroplasts are organelles found in plant cells and eukaryotic algae which conduct photosynthesis.

Related Topics:
Organelle - Plant - Cells - Eukaryotic - Alga - Photosynthesis

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Chloroplasts are similar to mitochondria but are found only in plants. Both organelles are surrounded by a double membrane with an intermembrane space; both have their own DNA and are involved in energy metabolism; and both have reticulations, or many foldings, filling their inner spaces.

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Chloroplasts convert light energy from the sun into ATP through a process called photosynthesis.

Related Topics:
ATP - Photosynthesis

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Chloroplasts are one of the forms a plastid may take, and are generally considered to have originated as endosymbiotic cyanobacteria.

Related Topics:
Plastid - Endosymbiotic - Cyanobacteria

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In green plants chloroplasts are surrounded by two lipid bilayer membranes, now thought to correspond to the outer and inner membranes of the ancestral cyanobacterium.

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The genome is considerably reduced compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities.

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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, where an 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 other eukaryotes, forming tertiary endosymbionts.

Related Topics:
Heterokont - Protist - Euglenozoa - Cercozoa

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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 the cell nucleus, and the protein gene products are trafficked to the chloroplast.

Related Topics:
Stroma - Cytoplasm - DNA - Ribosome

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Within the stroma are stacks of thylakoids, the sub-organelle 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 surface of the thylakoid.

Related Topics:
Thylakoid - Granum

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The photosynthetic proteins in the membrane bind chlorophyll, which is present with various accessory pigments. These give chloroplasts their green colour.

Related Topics:
Chlorophyll - Pigment

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Algal chloroplasts may be golden, brown, or red and show variation in the number of membranes and the presence of thylakoids.

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