The Use of Water in Biological Organisms

Water is considered to be one of the most important biochemical molecules on Earth, forming the majority of all living organisms. Almost 75% of the Earth’s surface is covered in water; evolutionists believe water to be the catalyst for all life where evolution has taken place for over four billion years to create all the beings that exist today. Williams [2000 p. 10] writes that 70% mass of a human cell and up to 95% mass of a plant cell comprise of water; the biological importance of this simple molecule is extremely significant as they require an aqueous environment. My aim is to examine and discuss the role of water in four different systems to demonstrate this statement.

The chemistry of water is quite simple: it comprises of one oxygen (O) atom covalently bonded to two hydrogen (H) molecules resulting with the chemical formulae H2O. Water contains 10 protons and 10 neutrons leaving it electrically neutral. However, as the nucleus of the oxygen atom attracts the electron of each hydrogen atom it makes the molecule polar. This intermolecular attraction of atoms (dipole) is known to allow formation of hydrogen bonds, which in large quantities are very robust in their lattice framework. This example of cohesion contributes to water’s thermodynamic properties. This high specific heat capacity gives rise to the highly differentiating temperatures of its three states of matter (gas at 100°c, solid at 0°c and liquid at standard temperature and pressure) which are vital in maintaining regulated environments for cells and organisms.

With this in mind, it is worth noting that cells have an optimal temperature and pH by which they can function as almost every chemical reaction in a cell is catalysed by a class of proteins called enzymes [Freeman & Co 2001 p. 71]. Enzymes are globular proteins comprising of long chains of polypeptides; they owe their tertiary structure to ionic bonds and disulphide bridges holding their primary structure in place to form their distinctive three-dimensional shape. They lower the activation energy (Ea‡) of reactions that are already energetically favourable to speed up the process.

Clark [2009 p. 183] states that enzymes are water soluble proteins; they contribute this characteristic to the ‘hydrophilic R-groups on the surface of the enzyme whereby hydrogen bonds are formed to the water molecules.’ The hydrophobic R-groups gather within the enzyme, demonstrating the ‘Oil Drop Model’ and their amphipathic status. This effect contributes to the creation of the enzyme’s tertiary globular structure, and demonstrates how water

Thermoregulation, or homeostasis (an autonomous body control system to maintain temperature and water levels) of a cell is made possible by the presence of an aqueous environment and the rate at which this provides kinetic energy to the enzyme results in its ability to bind to its substrate and create an enzyme/substrate complex. Too little kinetic energy means less frequency of enzyme and substrate collisions, lowering the reaction rate. Too high of a temperature and the enzyme structure begins to denature, the hydrogen and ionic bonds begin to break. The active site will eventually be unable to accommodate a substrate and the enzymes function will be diminished. Overall, we can see a direct link between the relationships of water, its thermal properties and its effect on chemical reactions.