Photosynthesis basic reactions

Without biological electron transfer reactions (also called reduction/oxidation or redox reactions) life would not exist. Well-organized electron transfer reactions in a series of membrane-bound redox proteins form the basis for energy conservation in photosynthesis and respiration. The basic reaction is simply the transfer of electrons from the donor to the final electron acceptor. Perhaps the best example of these redox reactions, their importance for living organisms, and the nature of the different type of biocatalysts that are involved is the respiration chain present in the membranes of mitochondria. The membrane-bound nature of this electron transport chain, supporting electron transfer from NADH to O2 as... 

The Basic Processes of Photosynthesis (Item Reactions 1, Table 17.1, Figure 17.3)... 

Write the basic reaction for photosynthesis in green plants. 

The basic reactions of photosynthesis and respiration involve in fact a series of uphill and downhill hydrogen transfers via sophisticated electron transport chains eventually resulting in the splitting of water into hydrogen and oxygen or in its synthesis from them. For our purpose, however, these reactions can be summarized in a simplihed manner in accord with the two overall equations ... 

Another important area is the use of photochemistry—chemistry that results from light absorption—to perform transformations that are not otherwise possible. The practical applications of photosynthesis were based on fundamental work to learn the new pathways that light absorption makes possible, but the work on these synthetic methods has also added to our basic understanding of the reaction mechanisms. The important natural process of photosynthesis also inspires some work in photochemistry, where the challenge is one of producing artificial photosynthetic systems that could use sunlight to drive the formation of energetic materials. 

Because the reaction requires energy from light, it is known as photosynthesis. The equation looks simple but photosynthesis is anything but that. The structures that are responsible for absorption of light in order for its energy to be used are the chlorophylls, which contain porphyrin-type ligands. The porphyrin structure is derived from the basic unit known as porphin, shown in Figure 22.16. 

Several metabolic pathways are described in later chapters. Basically, these are seqnences of chemical reactions leading from some molecnlar starting point to some distinct end point. Photosynthesis and respiration provide two examples. 

The AH values for these two reactions are negative, indicating that these reactions are exothermic. In both of these reactions, the products are formed from their basic elements so the AHs represent heats of formation. The third reaction is the familiar reaction for photosynthesis. The energy needed for this endothermic reaction is supplied by the sun. 

The respiration reaction is, basically, the opposite of the photosynthesis reaction. During respiration, glucose within the cells reacts with oxygen to produce carbon dioxide, water, and energy. 

As discussed above, the photosynthetic reaction center solves the problem of rapid charge recombination by spatially separating the electron and hole across the lipid bilayer. In order to achieve photoinitiated electron transfer across this large distance, the reaction center uses a multistep sequence of electron transfers through an ensemble of donor and acceptor moieties. The same strategy may be successfully employed in photosynthesis models, and has been since 1983 [42-45]. The basic idea may be illustrated by reference to a triad Dj-D2-A, where D2 represents a pigment whose excited state will act as an electron donor, Di is a secondary donor, and A is an electron acceptor. Excitation of D2 will lead to the following potential electron transfer events. 

Whilst thermolyses have aspects in common with photolyses, redox reactions are closely related to radiation reactions, in that they involve electron-transfer reactions. Electron-transfers, like proton transfers, can be extremely fast processes, and are therefore often key steps in biochemical systems. Probably the best understood example is that of photosynthesis, but there are many others not involving initial light absorption. The basic process is [2.19], but this... 

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