Water is a vital part for the function of organisms, as it is involved in the “energetics” of molecular interactions and conformational adaption of macromolecules in animal and plant cells, due to its structure, flexibility and several unique properties (Rand, 2004).
In an organism’s cell, various types of water are present. They are known as bound, hydration, vicinal and bulk water. 95% of watery body fluid is composed of bulk water, since they function as “space filling medium”, which supports life and creates an aqueous medium for cellular reactions (Watterson, 1987) .
Water as a “space filling medium”, also aid to assemble molecules, hence they can “achieve a configuration of lower free energy” (Rand, 2004).
Water’s effect on the functions of biological molecules, is due to the properties of water; which results from its unique structure and the way this structure allows water to form hydrogen bonds. Water molecules consist of two hydrogen atom and an oxygen atom, joined by a covalent bond. As the oxygen atom is more electronegative than hydrogen atom, it draws the electrons involved in the covalent bond, towards itself. This result in uneven distribution of electrons throughout the molecule, causing polarity within the molecule as the area around the hydrogen is slightly positive and the area around the oxygen is slightly negative. However, these charges are equal, so water molecule has no overall charge (Brooker et al., 2007).
As water is a polar molecule, it is an excellent transport medium, since it can dissolve and interact with a wide range of “polar and charged molecules” (Gerstein & Levitt, 1998), such as, water in the interstitial fluid, dissolves oxygen and carbon dioxide in blood, to be transported around the organism. Furthermore, as CO2 concentration builds up, water combines with the dissolved carbon dioxide, catalysed by carbonic anhydrase, to form H2CO3. This dissociates to form H+ and HCO3 - , which acts as buffer in blood plasma, keeping the pH constant for efficient enzyme activity. The dissociation occurs, because water has a slight tendency to ionize (Brooker et al., 2007). Ionic substances, such as, enzymes and hormones dissolve in body fluids, causing the electrostatic attraction between them to decrease, thus increasing their solubility.
In metabolic processes such as in a hydrolysis reaction, water acts as a reactant; where the electron-rich oxygen acts as a nucleophile. For example, hydrolysis of polysaccharides, e.g., sucrose, to form monosaccharides, e.g., fructose and glucose, and these are utilized by the body for various functions. Hydrolysis reaction releases energy so they are favourable, since the entropy of the system is increased. For instance, when energy is needed; water is required to hydrate ATP to release the energy. Water is also essential in oxidation-reduction reactions, e.g., respiration (Brooker et al., 2007).
Water is a stable medium, for efficient enzyme activity, due to the...