Role of water in photosynthesis

Photosynthesis is perhaps the most important biochemical pathway known ever. Almost aU life depends on it. Higher plants, algae, some bacteria, and a few protists and organisms are mostly responsible for this photosynthesis process and are collectively referred to as photoautotrophs [21]. In this process water coupled with carbon dioxide plays a central role in the synthesis of sugar from light, with oxygen as a side product. 

Two water molecules are oxidized by four consecutive charge-separation reactions through photosystem II to form a molecule of diatomic oxygen and four hydrogen ions. The outcoming electron in each step is transferred to a redox-active tyrosine residue followed by the reduction of a photoxidized 

In the light-independent or dark reactions the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase oxygenase) consumes CO2 from the atmosphere and in a complex process called the Calvin-Benson cycle releases three-carbon sugars that are subsequently combined to form glucose. 

An aspect we have repeatedly emphasized is the consumption, as a chemical, of water molecules in biological processes. This is important as we know that lack of continuous input of water into our body can cause many serious illnesses. This consumption of water largely occurs in enzymatic reactions, in protein synthesis, and many other crucial processes. This is different from other stabilizing or lubricating effects of water. 

In the next few chapters we shall discuss the role of water in biopolymers and self-organized assemblies. 

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