Light reactions

thumb|300px|Photophosphorylation in the light-dependent reactions of [[photosynthesis, which occurs at the thylakoid membrane in chloroplasts and cyanobacteria.]] In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation. Cyclic photophosphorylation occurs in both aerobic and anaerobic conditions, driven by the main source of energy available to living organisms, which is sunlight. All organisms produce ATP, which is the universal energy currency of life. In photophosphorylation, light energy is used to pump protons acr

chemical reactions involved in photosynthesis induced by light

Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. Photosystems are found in the thylakoid membranes of plants, algae, and cyanobacteria. These membranes are located inside the chloroplasts of plants and algae, and in the cytoplasmic membrane of photosynthetic bacteria. There are two kinds of photosystems: PSI and PSII. center|thumb|650x650px|Model of a photosystem and how it uses light energy to carry out process

photosystem that contains a pheophytin-quinone reaction center with associated accessory pigments and electron carriers

Plastoquinone (PQ) is a terpenoid-quinone (meroterpenoid) molecule involved in the electron transport chain in the light-dependent reactions of photosynthesis. The most common form of plastoquinone, known as PQ-A or PQ-9, is a 2,3-dimethyl-1,4-benzoquinone molecule with a side chain of nine isoprenyl units. There are other forms of plastoquinone, such as ones with shorter side chains like PQ-3 (which has 3 isoprenyl side units instead of 9) as well as analogs such as PQ-B, PQ-C, and PQ-D, which differ in their side chains. The benzoquinone and isoprenyl units are both nonpolar, anchoring the m

molecular unit responsible for absorbing light in photosynthesis

class of protein complexes, the second protein complex in photosynthetic light reactions

thumb|right|350px|Resonance (chemistry)|Resonance structures of a semiquinone Semiquinones (or ubisemiquinones, if their origin is ubiquinone) are free radicals resulting from the removal of one hydrogen atom with its electron during the process of dehydrogenation of a hydroquinone, such as hydroquinone itself or catechol, to a quinone or alternatively the addition of a single hydrogen atom with its electron to a quinone. Semiquinones are highly unstable.

Complex that transfers electrons from reduced plastoquinone to oxidized plastocyanin and translocates protons from the stroma to the lumen

site of water-splitting in photosynthesis

light re-emitted by chlorophyll molecules during return from excited to non-excited states

P680, or photosystem II primary donor, is the reaction-center chlorophyll a molecular dimer associated with photosystem II in plants, algae, and cyanobacteria, and central to oxygenic photosynthesis.

P700, or photosystem I primary donor, is a molecular dimer of chlorophyll a associated with the reaction center of photosystem I in plants, algae, and cyanobacteria.