RE: What specifically is the role of P680 in photosynthesis
Photosystem I is arranged around a molecule of chlorophyll a with a peak absorption at 700nm.
(either chlorophyll P700 or P680) ..
Cyclic electron flow takes photoexcited electrons on short-circus pathway
Travel from P680 transport chain to P700 then back to P680
Main aspect of light-independent reactions
Produces PGAL (phosphoglycerdehyde)
Carbon (in form CO2) enters through stomates of leaf and becomes fixed into PGAL
Occurs only in the light
Carbon fixation occurs in Calvin Cycle
Reduction reaction since Carbon gains hydrogen
CO2 enters the cycle and becomes attached to 5-carbon-cycle (RuBP)
Very unstable so it breaks down to 3-PGA
In most plants, when CO2 enters the Calvin Cycle it is fixed into 3PGA by rubisco
When rubisco binds with O2 instead of CO2, this diverts photosynthesis in two ways:
The PS II reaction centre is significantly more complex than thereaction centre of PS I, where P700 is clearly localised on thegreen complex CP I. P680, the reaction centre chlorophyll of PSII, is difficult to determine because the P680+ Pheo- charge separation decays within a nanosecond.P680 is currently considered to be a chlorophyll- dimer, at least in the ground state.
P700 - Biology-Online Dictionary
The nature of the reaction centre of chlorophyll, P700, is stillunknown, as there is conflicting evidence. It has been suggestedthat this could be explained if there is a pair ofelectronically interacting chlorophyll- molecules in the ground(reduced) state (P700), and that the unpaired electron of theP700+ (oxidised) state is localised on only one of thechlorophyll's (). The other 40 to 50 chlorophyll- molecules ofCP I act as antennas, and are thought to be responsible for the721nm fluorescence emission maximum (,).
Improved extraction procedures gave oxygen evolving PS II(photosystem II) particles (BBY's). These particles are largepieces of granal membranes, probably lipid depleted (,, ,). Other treatments have been employed to isolatethe core particles from PS II. These core particles contain tworeaction chlorophyll- proteins, CP 47 and CP 43 and several nonchlorophyll binding (D1, D2), but are free fromchlorophyll + complexes. Core particles which retain manganesehave been successfully isolated with the two chlorophyll-proteins and a limited number of other polypeptides. CP 47 andCP 43 can be purified from the other components of PS II by theuse of SDS-PAGE or HPLC (high performance liquid chromatography)but they have no photochemical activity in isolation.
This process uses only Photosystem I and the chlorophyll P700.
Initial experiments done by Ogawa ()and Thornber () isolatedtwo complexes by SDS-PAGE from SDS-solubilised membranes. One ofthese complexes, CP I, had a high apparent molecularweight and contained only chlorophyll-. CP I is the most stableof the complexes and retained the photochemical activity ofP700, the reaction centre of chlorophyll in PS I. It has achlorophyll to P700 ratio of ~45 (, , ,, ) and abeta-carotene to P700 ratio of ~8.
This figure shows a schematic representation of the majorsubfractions that can be isolated from membranes. InPS I (photosystem I) an initial solubilisation produces largeparticles (called PS I-110). These particles contain twochlorophyll-protein complexes: the reaction centre chlorophyll-protein (CP I) and a chlorophyll + complex (LHC I,light-harvesting complex) (). PS I-110 also contains 6 to 8 of lower molecular weight (8 to 25kDa, where 1dalton=1 a.m.u.) that do not bind to chlorophyll, calledSubunits II-VII. CP I, the reaction centre P700 chlorophyll-protein, can be isolated from any of these mixtures by treatmentwith SDS (sodium dodecyl sulfate) or LiDS (lithium dodecylsulfate) followed by electrophoresis.
P680 and P700 They both appear ..
The reaction centers of these photosystems are P700 and P680, ..
PS1 is P700 and PS 2 is P680 noncyclic photophosphorylation you see
P700 - Wikipedia
The reaction centre is P700 The reaction centre is P680
P700 See also: photosystem II.
in the form referred to as P700
The above sketch of the cyclic process is patterned after a visualization in Moore, et al. Two photons from either the red or blue end of the spectrum fit the sensitive response of the . They are captured by the and transferred to the Photosystem I reaction center, which contributes two high energy electrons to the primary electron receptor. They are passed to ferrodoxin (Fd), an iron containing protein which acts as an electron carrier. A second electron carrier plastoquinone (Pq) carries the electrons to a complex of two cytochromes. In the process, energy is provided to produce a proton gradient across the membrane which can be used for the ADP to ATP conversion. The electrons are returned by plastocyanin (Pc) to the P700 pigment in the reaction center to complete the cycle.
(PS I) contains a reaction center chlorophyl (P700) ..
The protein complex that constitutes Photosystem I contains eleven , six of which are coded in the nucleus and five are coded in the . The core of Photosystem I contains about 40 molecules of chlorophyll a, several molecules of beta carotene, lipids, four manganese, one iron, several calcium, several chlorine, two molecules of plastoquinone, and two molecules of pheophytin, a colorless form of chlorophyll a .(Moore, et al.)
The excited electrons are transferred from P700 to a FeS protein ..
refers to the use of light energy to ultimately provide the energy to convert ADP to , thus replenishing the universal energy currency in living things. In the simplest systems in prokaryotes, photosynthesis is used just for the production of energy, and not for the building of any biological molecules. In these systems there is a process called cyclic photophosphorylation, which just accomplishes the ADP to ATP process for immediate energy for these cells. This process uses only and the chlorophyll P700.
At the center of Photosystem I is a pair of chlorophylls called P700
The light absorption processes associated with take place in large protein complexes known as photosystems. The one known as Photosystem II contains the same kind of as but in a different protein environment with an absorption peak at 680 nm. (It is designated P680). The binding protein for PSII is much smaller than that for PSI, about 47,000 compared to 110,000. It resonates from energy transmitted by about 250 chlorophyll a and b in equal numbers. Its core contains xanthophylls but no beta carotene (Moore).
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