Biological Significance of Water - Essay Example

Biological Significance of Water Structure of Water In many ways, water is a miracle liquid. Water is found on the earth in three forms: solid, liquid and gas; or ice, liquid water and gas respectively. It is essential for all living things and it is often referred to as a universal solvent because many substances dissolve in it. These unique properties of water result from the ways in which individual H2O molecules interact with each other. Arrangement of electrons in H2O Water is the chemical substance with chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Oxygen attracts electrons much more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom. The presence of a charge on each of these atoms gives each water molecule a net dipole moment. Electrical attraction between water molecules due to this dipole pulls individual molecules closer together, making it more difficult to separate the molecules and therefore raising the boiling point. This attraction is known as hydrogen bonding. Water can be described as a polar liquid that dissociates disproportionately into the hydronium ion (H3O+(aq)) and an associated hydroxide ion (OH(aq)). Water is in dynamic equilibrium between the liquid, gas and solid states at standard temperature and pressure, and is the only pure substance found naturally on Earth to be so. Properties of water Tasteless, colorless, odorless liquid Water is a tasteless, odorless liquid at ambient temperature and pressure, and appears colorless in small quantities. Lower melting point and higher boiling points Water's has a melting point of zero degrees and boiling point of 100 degrees Celsius respectively. These properties are higher than would be expected based on similar compounds. Thus, water remains a liquid under a higher range of temperature compared to other compounds. As a result, plants and animals do not start freezing at lower temperatures or boiling at higher temperatures. Viscosity Because of its comparatively smaller molecular weight, it is unusually viscous. Water has the ability to act as either an acid or a base depending on the circumstances, and by its nature it is perfectly neutral (it's the standard for balance between acids and alkalines [bases]). Universal Solvent Water is the most universal of solvents and though polar in its make up, it exhibits properties that indicate a sort of polymerizing link between its molecules similar to heavier organic non-polar compounds. Existence in three forms: solid, liquid, gas It exists on earth in all three basic states, solid, liquid, and gas, High Heat capacity Water is also extremely useful due to its high heat capacity. It has an enormous ability to absorb and transmit energy. For example the amount of energy it would take to melt 1 kilogram of ice at zero degrees Celius would be enough to lower the temperature of 1 kilogram of Aluminum over 570 degrees Celsius. While the amount of heat it would take to melt that kilogram of ice, heat it and boil away, 720 Calories, would be enough to raise that same amount of Aluminum to its melting point! This is why water is ideal as a insulation or a heat dissipation source. It holds more heat than just about anything. Easily reacts with other compounds Water reacts with more substances than any other compound. It reacts physically with several compounds to add to their crystal structure. Compounds like copper and magnesium sulfate are two examples of many compounds that almost always found in nature with water molecules physically attached to their crystal structure. These type of compounds are often "dried out" or dehydrated and used to absorb water from their surroundings. Some of these compounds, have water as such an important part of their structure that they will even extract all available moisture from the air. These compound are natural dehumidifiers, dependent on water to complete their structure. Water also reacts chemically with many substances, creating new substances or compounds. Water is also a source of hydrogen and oxygen for chemical reactions. Range of Functions of Water in Living Beings Water forms a major part of the body weight Water makes up a major portion of the body weight of living beings. eg.in human beings, 90% of the body weight is composed of water. Major component of Body fluid Water is a major component of the body fluid, whether in plants or animals. In animals, it a part of the blood and cells. It fills spaces between cells and is responsible for transport of food from one part of the plant/animal to another. In plants, it is part of the phloem, and responsible for transport of food to different parts of the plant. As water is such a good solvent, it almost always has some solute dissolved in it, most frequently a salt. Being a good solvent, it is responsible for carrying food and oxygen to various parts of the body of plants and animals. Provides turgidity to the plants. When water is carried through xylem up stems in plants the strong intermolecular attractions hold the water column together. Strong cohesive properties hold the water column together, and strong adhesive properties stick the water to the xylem, and prevent tension rupture caused by transpiration pull. Other liquids with lower surface tension would have a higher tendency to "rip", forming vacuum or air pockets and rendering the xylem water transport inoperative. Helps maintain the electrolyte balance Water helps maintain the electrolyte balance in the body of plants and animals. The water in the body of plants and animals has dissolved minerals, which are in turn essential for metabolism in the plant/animal. These minerals are mainly Sodium, Potassium and Calcium, the quantity of which must be balanced and relatively constant in the body. Helps store/maintain heat High heat capacity of water makes it a good source of storing/maintaining heat in the body of animals. As water has a high specific heat capacity, a lot of energy is required to change its temperature by a few degrees. Thus, when plants and animals are subjected to changes n environmental temperature or extremes of temperature, it is the water component in the body, which helps the living being retain its body temperature and stay alive. Capillary action helps in movement of fluids Capillary action of water helps body fluids move in the body, sometimes against gravity, which would otherwise have not been possible. It is this very capillary nature of water, which helps in the transport of energy and essential electrolytes in the body of both plants and animals. Surface tension helps in movement There are various life forms which make use of the surface tension property of water for their movement. Water molecules play an invaluable role in governing the structure, stability, dynamic, and function of biomolecules like proteins and nucleic acids. Proteins and nucleic acids play important biological functions: they catalyze and regulate reactions, transport substrates, code and transcribe genetic information.. Indeed, they lack activity in the absence of water. The hydrophobic effect and hydrogen bonds are also of prime importance and water is an actor in these contributions to protein structure and stability The hydrophobic effect is generally considered to be the major driving force for the folding of globular proteins. It results in the burial of the hydrophobic amino acid side-chains in the core of the protein. Based on the work of Frank and Evans [10], which explains at the molecular level the low solubility of non-polar species in water, Kauzmann introduced already in the late 1950's the concept of 'hydrophobicity' to explain the complexities of protein folding [11]. Water tends to form ordered cages around non-polar groups (hydrophobic hydration) which leads to a decrease in entropy of the system. These water molecules gain entropy when they are released after hydrophobic surfaces are put in contact with each other. This contributes in a very favorable way to the free energy of stabilisation of the protein. Water is therefore fundamental in protein folding because of its role in defining hydrophobic attractions. The hydrophobic "collapse" of the protein is necessarily accompanied, and guided, by hydrogen-bond formation between favorable functional groups [12]. A hydrogen bond (H-bond) occurs when two electronegative atoms, such as nitrogen and oxygen, interact with the same hydrogen. Along with hydrogen bonding between base-pairs and London dispersion forces between the stacked bases, water contributes to the stabilization of RNA and of DNA structures. The role of water in the stabilization of the 3D structure of nucleic acids is even more important than in proteins because of the presence of negatively charged phosphate groups. References http://vava.essortment.com/watersolventhy_rgqx.htm http://en.wikipedia.org/wiki/Water_(molecule) http://www.merck.com/pubs/mmanual_ha/sec3/ch18/ch18a.html http://www.exobio.cnrs.fr/spip.phparticle44 Read More