Biochemistry Module Overview
The Chemicals of Life Carbohydrates Lipids Water Proteins Nucleicacids
Water Life as we know it on earth cannot supply without a regular supply of water. Water has many important properties, the most remarkable of which is that it is actually a liquid: similar molecules like methane and hydrogen sulphide are gases at STP. This is due to the polar nature of the water molecule, which causes hydrogen bonding between neighbouring molecules, resulting in water having a higher than expected boiling point.
Biological roles of water 1. As a solvent Water is an efficient solvent, not just for ionic salts but also for polar molecules such as sugars.
Biological roles of water 2. As an insulator Water has a maximum density when it is just above its freezing point. Ice layers therefore float and insulate the water below the surface of ponds and lakes.
Biological roles of water 3. Moderator of temperature changes. Water absorbs a lot of heat when changing state. Loss of heat through evaporation cools us when we sweat.
Biological roles of water 4. As a transport medium It’s hydrogen-bonding and solvent properties make water important as a transport medium for living things
Biological roles of water 5. As a reagent Water is an important reactant in some chemical reactions, particularly hydrolysis.
Proteins Proteins are an extremely important and varied class of molecule. They are condensation polymers synthesised from amino acid monomer units.
Biological roles of proteins 1. As structural molecules, adding strength/flexibility to tissues such as hair and bone. 2. As enzymes, controlling the reactions within cells. 3. As antibodies and hormones. 4.As components of cell membranes.
Enzymes Enzymes are proteins that act as biological catalysts. Without them , the reactions that make life possible would be too slow for life to exist.
Properties of enzymes 1. Show great specificity, only catalysing reactions involving a particular molecule or class of molecule. 2. Control the specificity of a reaction in such a way as to produce ‘clean’ reactions with very few by-products. 3. Are extremely sensitive to changes in conditions such as temperature or pH. 4. Are extremely sensitive to the presence of cofactor and inhibitor molecules. 5. Are far more efficient than inorganic catalysts.
Carbohydrates A group of structurally-related molecules that provide living organisms with energy: that is, they act as fuels. They are made of only carbon, hydrogen and oxygen.
Carbohydrate groups 1. Monosaccharides – simple sugars with the formula (CH2O)n. They provide instant-access energy and act as structural units for many polysaccharides. 2. Disaccharides – dimers of monosaccharides, which function as transport molecules for monosaccharides in organisms and as structural units in some polysaccharides. 3. Polysaccharides – condensation polymers of monosaccharides or disaccharides used for energy storage and as structural components of cells.
Lipids Lipids play essential roles in cell structure and metabolism. They are grouped together because they are insoluble in water, but there are distinct molecular types: triglycerides, phosphoglycerides and steroids.
Lipid groups 1. Triglycerides occur in animal fats (solid at STP) and vegetable oils (liquid at STP). Fats and oils are the major stores of metabolic energy in animals and plants. 2. Phosphoglycerides are important components of cell membranes. In water, they can group together to form a bilayer, which is the fundamental structure of cell membranes. 3. Steroids are a series of biologically important molecules, including cholesterol, testosterone, oestrogen and cortisone.
Nucleic acids The nucleic acid DNA (deoxyribonucleic acid) carries all of an organisms genetic information at a molecular level. RNA (ribose nucleic acid) does a similar job in some viruses and is involved in protein synthesis in all organisms.
Properties of DNA 1. It is a self-replicating molecule i.e. it can make exact copies of itself. 2. It is capable of passing genetic information intact from one generation to the next. 3. It contains the information needed to synthesise proteins.