With reference to membrane proteins, discuss the important role of water in defining the shape and function of biomolecules.

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Title: With reference to membrane proteins, discuss the important role of water in defining the shape and function of biomolecules.  

Water plays an important role in defining biomolecules shape and function because it possesses some unique properties.  Among these properties the ability to form hydrogen bond and hydrophobic effect contribute most to the shape and function determination of biomolecules.  

Water is a polar molecule. The hydrogen atoms take on a slight positive charge and the oxygen atom takes on a slight negative charge due to unequal sharing of electrons. A hydrogen bond is an interaction between a covalently bonded hydrogen atom on a donor group and a pair of nonbonded electrons on an acceptor group.  Water itself also form H-bond between the adjacent water molecules in order to add stability. Molecules with groups capable of forming H-bond and readily dissolves in water are called hydrophilic. Due to the polar nature and the ability to form hydrogen bond make water a very versatile solvent.  This is very important role of waters in biomolecules since most of the chemical reactions that occur in organism require material dissolved in water.  The high H-bonding capacity allow it to act a non-electrolytes and dissolve polar compound such as glucose in the body. Water can also act as electrolytes due to the high capacity of hydration shells and high dielectric constant.  This allows inorganic ionic material such as NaCl to become hydrated and dissolve in water.  It can also act as polyelectrolytes where particles are in a colloidal suspension by hydrated surface ionic charge and an example of this is globular proteins.  

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Substances like lipid which are nonpolar and nonionic are not able to form hydrogen bonds with water and therefore they show very limited solubility in water.  These substances are called hydrophobic.  They form a clathrate structure where all the hydrophobic molecules tends to cluster together in order to reduce the entropy of the mixture.  Most of these biomolecules are amphipathic molecules which contain a head group that is strongly hydrophilic and coupled to a hydrophobic tail.  

This is very important feature in defining the shape and function of biomolecules especially in phospholipid membrane, globular protein structure and membrane ...

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