Photosynthesis is a biochemical process by which plants and certain bacteria capture sunlight and convert it to chemical bond energy. The end result of this process is the reduction of atmospheric carbon dioxide into sugars that are subsequently used for metabolic activities within the cell. In primitive photosynthetic bacteria, the electrons that are required for the reduction of CO2 are derived from organic molecules and inorganic sulfide. These bacteria do not liberate oxygen as a by-product of photosynthesis, and hence are termed anoxygenic. Plants and cyanobacteria contain a unique cluster of manganese atoms that is capable of splitting water to produce electrons for carbon fixation, liberating oxygen in the process. Oxygenic photosynthesis employs two reaction centers in series, termed Photosystem II and Photosystem I, to achieve transmembrane electron transfer. The photosynthetic process starts when a chlorophyll pigment molecule in either reaction center absorbs a photon of sunlight and rapidly transfers the energy to a trapping center composed of special pairs of chlorophylls. This is followed by charge separation between the primary donor and the primary acceptor molecules and subsequent electron transfer through a chain of redox cofactors. The reducing power of the electron is stored as NADPH and used along with the ATP, generated by a concomitant proton gradient, to fix CO2 via a scheme known as the Calvin-Benson-Bassham cycle.
All Science Journal Classification (ASJC) codes
- Immunology and Microbiology(all)