The chlorophyll molecule consists of a flattish fairly square section composed of
5-membered pyrrole rings
: (grey) with double C-C bonds, inside which are 4 nitrogens
(blue), and a central magnesium atom (lime green)
This porphyrin structure is similar to the haem group in haemoglobin and myoglobin, which have an iron atom in the centre.
Leading off from one corner is a long chain of carbon and hydrogen atoms
called the phytol chain, a 20-carbon diterpene alcohol section which enables the chlorophyll molecule to be anchored in the membrane of the chloroplast. If plant material is eaten, this section of the molecule may be removed and incorporated into vitamin E and K(1).
There are several forms of chlorophyll. This molecule is in fact chlorophyll A. Chlorophyll B, which has 2 closer absorption peaks, has an aldehyde -CHO group off to one side of the porphyrin structure, instead of the methyl group
In photosynthesis, the function of chlorophyll is to absorb photons of light energy and to emit electrons. These are then passed to electron acceptors which pass on their energy to be used in the production of ATP and reduced NADP. These compounds are then used to reduce carbon dioxide in the light-independent reactions of photosynthesis.
The loss of electrons from chlorophyll is repaid using electrons taken from water during the process of photolysis.