ABSTRACT
Most natural photosynthetic systems utilize chlorophylls to absorb light energy and carry out photochemical charge separation that stores energy in the form of chemical bonds. All photosynthetic organisms contain antenna systems, which increase the photon collection ability, and reaction center complexes, which carry out the actual photochemistry. All these components are bound to proteins in well-defined sites with unique positions. The reaction center complexes are always integral membrane proteins that are embedded in biological membranes. Antenna complexes are always attached to the membrane and may also be integral membrane proteins. The antenna complexes transfer energy to the reaction center using a Förster resonance energy transfer mechanism. The reaction center contains a special pair of chlorophylls, which act as a primary electron donor. When excited, they transfer an electron from the excited state to a nearby electron acceptor molecule. After the primary photochemistry, the electron and the hole are separated by an ultrafast series of chemical reactions that separate the charges and stabilize them against recombination. Long-term storage of energy takes place with the formation of adenosine triphosphate (ATP), reduced form of nicotinamide adenine dinucleotide phosphate (NADPH), and ultimately sugars.
