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.
Light reaction and photophosphorylation
Photosystems are of two types: PS I P700, PS II P680. Components of photosystem I and II transfer the electrons from water to NADP. Light is absorbed by these photosystems and electrons are transferred from water to NADP. Photophosphorylation is a process where the light energy captured by the photosynthetic organisms is transformed into the phosphate bond energy of ATP. During the transfer of electrons, ATP is synthesized. Electron flow is cyclic. As a result oxygen is not released and ATP is formed as a result of proton gradient created by Cytochrome bf pump.
Photosynthesis is a process where by energy from light is harvested and used to drive synthesis of carbohydrates from carbon dioxide and water. Photophosphorylation is a process where the light energy captured by the photosynthetic organisms is transformed into the phosphate bond energy of ATP. Components of photosystem I and II transfer the electrons from water to NADP. Second step of photosynthesis is called Calvin’s cycle and it is a dark reaction. There are two stages here, I and II. Stage I is carbon dioxide fixation and stage II is the regeneration phase. Photorespiration is the process wherein oxygen consumption occurs in illuminated temperature zone of plants under high oxygen and low carbon dioxide. C4 cycle is the pathway adopted by C4 plants to conserve the carbon dioxide released via photorespiration. It occurs in mesophyll cells.
Photosynthesis is the process by which phototrophs convert carbon
dioxide and water into simple carbohydrates and oxygen in the presence
of chlorophyll, using sunlight.
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.
The overall equation for photosynthesis can be summarised as below:
But now it is known that photosynthesis is a two stage process.
The excited electron may instead be used to provide the reducing power
needed in the second, light-independent stage of the photosynthetic
In areas where
light is insufficient for this process of photosynthesis to occur,
then other measures have to be taken by the plant to maintain a steady
rate of producing chemical energy to survive.
The whole process
takes place all the time during the hours of daylight, but only the
light-independent reactions of photosynthesis are sometimes referred
as the dark reactions (however this does not mean they only occur in
the dark, where as in fact they occur continuously).
Photosynthesis is summarised by the
However this equation is somewhat miss leading, as photosynthesis is a
Basic process of photosynthesis
Photosynthesis is a process where by energy from light is harvested and used to drive synthesis of carbohydrates from carbon dioxide and water.
Chlorophyll's most important use, however, is in nature, in .It is capable of channelling the energy of sunlight into chemical energythrough the process of photosynthesis. In this process the energyabsorbed by chlorophyll transforms carbon dioxide and water intocarbohydrates and oxygen:
(The process of photosynthesis is explained
in more detail in my prediction)
Although light intensity seems to be the major factor affecting the
size of ivy leaves, there may have been some influence from other
abiotic factors that have also been measured and taken into account in