P700
Encyclopedia
P700, or Photosystem I primary donor, (where P stands for pigment) is the reaction-center
chlorophyll a
molecule in association with photosystem I
. Its absorption spectrum peaks at 700 nm. When photosystem I absorbs light, an electron is excited to a higher energy level
in the P700 chlorophyll. The resulting P700 with excited electron is designated P700*, and is the strongest biological reducing agent (in contrast to P680
+ of photosystem II
, the strongest biological oxidizing agent). The electron is subsequently captured by the primary electron acceptor. Type I photosystems use ferredoxin
-like iron-sulfur cluster proteins as terminal electron acceptors.
Photosystem I is more complex than photosystem II (P680
), as it has a more complex antenna system, has more subunits in its overall structure, and may exhibit cyclic or non-cyclic electron transfer from the excited P700* to the electron acceptor.
Photosynthetic reaction centre
A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors assembled together to execute the primary energy conversion reactions of photosynthesis...
chlorophyll a
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
molecule in association with photosystem I
Photosystem I
Photosystem I is the second photosystem in the photosynthetic light reactions of algae, plants, and some bacteria. Photosystem I is so named because it was discovered before photosystem II. Aspects of PS I were discovered in the 1950s, but the significances of these discoveries was not yet known...
. Its absorption spectrum peaks at 700 nm. When photosystem I absorbs light, an electron is excited to a higher energy level
Energy level
A quantum mechanical system or particle that is bound -- that is, confined spatially—can only take on certain discrete values of energy. This contrasts with classical particles, which can have any energy. These discrete values are called energy levels...
in the P700 chlorophyll. The resulting P700 with excited electron is designated P700*, and is the strongest biological reducing agent (in contrast to P680
P680
P680, or Photosystem II primary donor, refers to any of the 2 special chlorophyll dimers , PD1 or PD2. These 2 special pairs form an excitonic dimer, which means that they behave in function as a single entity; i.e., they are excited as if they were a single molecule...
+ of photosystem II
Photosystem II
Photosystem II is the first protein complex in the Light-dependent reactions. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. The enzyme uses photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce...
, the strongest biological oxidizing agent). The electron is subsequently captured by the primary electron acceptor. Type I photosystems use ferredoxin
Ferredoxin
Ferredoxins are iron-sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co...
-like iron-sulfur cluster proteins as terminal electron acceptors.
Photosystem I is more complex than photosystem II (P680
P680
P680, or Photosystem II primary donor, refers to any of the 2 special chlorophyll dimers , PD1 or PD2. These 2 special pairs form an excitonic dimer, which means that they behave in function as a single entity; i.e., they are excited as if they were a single molecule...
), as it has a more complex antenna system, has more subunits in its overall structure, and may exhibit cyclic or non-cyclic electron transfer from the excited P700* to the electron acceptor.