Why Chloroplasts Are Important Photosynthetic Organelles?

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Chloroplasts are important photosynthetic organelles that present in plant cells. It is believed that chloroplasts evolve from an endosymbiotic event; engulfment of a photosynthetic cyanobacterium by a large heterotrophic host cell (1, 2). During this process proteins in the cyanobacterium has been transferred to the nucleus and also the proteins that are essential for organelle biogenesis has been transferred to the cyanobacterium making it dependent on the host. Although chloroplast proteins have estimated to consist of 3500-4000 different types of polypeptides, the protein coding capacity in chloroplast genes is approximately 200 polypeptides (3, 4). This data further suggest that most of the proteins found in chloroplast are encode by nuclear genome and transport to the chloroplast. At least, a few proteins are use secretory pathway in which first targeted to the endoplasmic reticulum and then transfer to the chloroplast through vesicles (5-7).
Chloroplasts are organized structures for photosynthesis and they consist of three distinct membranes. They are outer membrane, inner membrane and thylakoid membranes. Photo complexes, photosynthetic proteins are assemble in the thylakoid membrane network. These three membranes separate three spaces in the chloroplast, namely, intermembrane space, stroma and thylakoid lumen. Protein targeting and translocation into chloroplast is therefore of broad interest.

A general outline of chloroplast protein import
According to the
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