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

Chloroplasts are one of the forms a plastid may take, and are generally considered to have originated as endosymbiotic cyanobacteria. 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. The genome is considerably reduced compared to that of free-living cyanobacteria, but the parts that are still present show clear similarities.

The fluid within the chloroplast is called the stroma, corresponding to the cytoplasm of the bacterium, and contains tiny circular DNA and ribosomeA ribosome is an organelle composed of rRNA (synthesized in the nucleolus) and ribosomal proteins. It translates mRNA into a polypeptide chain (e. a protein). It can be thought of as a factory that builds a protein from a set of genetic instructions.s, though most of their proteins are synthesized by the cell nucleus. Within the stroma are stacks of thylakoidA thylakoid is part of an internal membrane system of chloroplasts folded repeatedly into a stack of disks called grana. Thylakoids have light absorbing pigments ( chlorophylls) and enzymes required to form ATP, NADPH, or both in photosynthesis. The stacks, 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.

The photosynthetic proteins in the membrane bind chlorophyllChlorophyll is the green photosynthetic pigment present in chloroplasts, which provides the energy necessary for photosynthesis. The intense green color of chlorophyll is due to its strong absorbence in the red and blue regions of the electromagnetic spec, which is present with various accessory pigmentIn biology, pigment is any material resulting in color in plant or animal cells which is the result of selective absorption. Some biological material has so-called structural color, which is the result of selective reflection or iridescence, usually dones. These give chloroplasts their green colour. Algal chloroplasts may be golden, brown, or red and show variation in the number of membranes and the presence of thylakoids.

1 See also

• Chloroplast membraneChloroplasts contain several important membranes, vital for their function. Like mitochondria, chlorplasts have a double-membrane envelope, called the chloroplast envelope . Each membrane is a phospholipid bilayer, between 6 and 8 nm thick, and the two ar
• Calvin cycleThe Calvin cycle (also known as Calvin-Benson cycle is a series of biochemical reactions taking place in the chloroplasts of photosynthetic organisms. It was discovered by Melvin Calvin and Andy Benson at the University of California, Berkeley. During pho