photosynthesis Biochemistry. Transformation of radiant energy in chemical

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The Photochemical work which is carried out at photosynthesis, finally is reduced to decomposition of molecules of water or its any analogue, for example H2S. However, before it will occur, ' physical ' energy of the caught photons should be somehow modified, transformed in ' chemical ' energy. In realisation of this stage of photosynthesis, i.e. A stage reduced to transformation of energy, only small part of all pigmentary molecules concentrated in fotohimicheski the active centres hloroplastov participates. Energy absorbed by a chlorophyll and other photoactivated pigments, is transferred to the molecules of a chlorophyll which are in these fotohimicheski the active centres, or traps. As a result separate elektronam energy enough is informed that they could pass from chlorophyll molecules in fotohimicheski the active centres to other molecules being nearby, to so-called carriers elektronov. The carrier absorbs a certain part of this energy of activation and transfers elektron to a following carrier where the same process repeats. In hloroplastah various carriers elektronov are placed on a membrane or in a membrane and form here a certain number in which limits they settle down according to their ability to attach elektrony (differently, from them ' in oxidation-reduction potential ').

Thus, elektron passes from one carrier to another just as water - from one ledge on another is overthrown on the cascade. During moving elektrona on such chain of carriers the part of its energy is translated in the chemical form as at the expense of this energy from adenozindifosfata (ADP) and inorganic phosphate (P1) it is synthesised adenozintrifosfat (ATR). In a chemical bond between ADP the energy significant amount (8-10 kcal/mol) and this energy also is reserved liberated in the course of reactions in which the specified communication is broken off. Synthesis ATR proceeding with use of energy of a visible part of solar radiation, carries the name fotofosforilirovanija. ATR is ' power currency ' live cages. Many reactions going in a cage with consumption of energy (endergonicheskie reactions), receive this energy as a result of disintegration ATR to ADP and or P1, or any another fosforilirovannogo connections.

More 20 years ago Robert Emerson has found out that red light with length of a wave more than 700 nanometers, rather ineffective in photosynthesis of the higher plants, becomes quite effective if to use it together with more short-wave red light. this phenomenon named ' effect of strengthening of Emerson ', was necessary in a hypothesis basis according to which photosynthesis includes two different light reactions and optimum conditions are created for it in that case when two these reactions proceed simultaneously. A hypothesis allocation from hloroplastov the higher plants of two separate systems which have received the names photosystem I and photosystem II (has supported fig. 4.12). Each of these photosystems is characterised by the special set of molecules of a chlorophyll and the carriers connected with them elektronov and everyone carries out the, photosynthetic reactions inherent only in it.

The Photosystem I - unique, available - works for bacteria without oxygen participation as bacteria are the most primitive avtotrofy; the photosystem I, apparently, prevailed at early stages of biological evolution when oxygen in terrestrial atmosphere was a little. With development of photosystem of II plant had an opportunity to allocate molecular oxygen from water. This circumstance, obviously, also has defined change of properties of terrestrial atmosphere: from anaerobnoj it became now aerobic.

A Chlorophyll which is a power trap of photosystem I, designate symbol Р700 as the absorption maximum is necessary at it on 700 nanometers. At absorption of quantum of light one of elektronov Р700 passes to higher power level. In this condition it is grasped by the fiber containing iron and sulphur (FeS), and then transferred to a carrier which is called ferredoksinom. Further elektron follows on one of two possible ways. one way (cyclic fotofosforilirovanie) consists of stage-by-stage carrying over elektrona from ferredoksina back to Р70о through a number of intermediate carriers among which are available flavoproteidy, containing vitamin В2, and gemsoderzhashchie tsitohromy. While elektron moves therefore to a cyclic way, its energy is used for joining P1 to ADP with formation ATR. Oxygen in cyclic fotofosforilirovanii does not participate, and as gas exchange between internal space of sheet and atmosphere does not occur, photosynthesis theoretically of this kind can proceed and at closed ustitsah. Cyclic fotofosforilirovanie - a unique functional way of photosynthesis to monochromatic light with length of a wave more than 700 nanometers because for activation of photosystem II more short-wave radiation is necessary. However it is for the present difficult to us to judge that, how much important role plays cyclic fotofosforilirovanie in leaves.