Chloroplast Membrane

Chloroplast Membrane

Chloroplasts contain several important membranes, vital for their function. Like mitochondria, chloroplasts have a double-membrane envelope, called the chloroplast envelope. Each membrane is a phospholipid bilayer, between 6 and 8 nm thick, and the two are separated by a gap of 10-20 nm, called the intermembrane space. The outer membrane is permeable to most ions and metabolites, but the inner membrane is highly specialised with transport proteins. Carbohydrates are transported across the outer membrane by a triose phosphate translocator. One or two additional membranes may enclose chloroplasts in algae.

The origin of chloroplasts is now largely accepted by the botany community as occurring via endosymbiosis on an ancestral basis with the engulfment of photosynthetic bacterium within the eukaryotic cell. Over millions of years the endosymbiotic cyanobacterium evolved structurally and functionally, retaining its own DNA and the ability to divide by binary fission (not mitotically) but giving up its autonomy by the transfer of some of its genes to the nuclear genome.