Biological Molecules

• Most of the molecules in living organisms fall into three categories: carbohydrates, proteins and lipids.
• Carbohydrates contain carbon, oxygen and hydrogen.
• Monosaccharides are simple sugars such as glucose(C6H12O6) or fructose.
• Glucose molecules contain lots of energy which can be released in respiration by breaking the bonds between the carbon atoms.
• Disaccharides are made when two monosaccharides join together, for example, maltose is formed from two glucose molecules, and sucrose is formed from one glucose and one fructose molecule.
• Polysaccharides are formed when lots of monosaccharides join together, for example, starch, glycogen or cellulose are all formed when lots of glucose molecules join together.
• Polysaccharides are insoluble and therefore useful as storage molecules.
• Most fats (lipids) in the body are made up of triglycerides.
• The basic unit of triglycerides is one glycerol molecule chemically bonded to three fatty acid chains.
• Fatty acids vary in size and structure.
• Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature).
• Proteins are formed from long chains of amino acids, there are 20 different amino acids, and when amino acids are joined together, a protein is formed.
• Preparing a food sample for testing involves breaking up the food using a pestle and mortar, transferring to a test tube and adding distilled water, mixing the food with the water by stirring with a glass rod, filtering the mixture using a funnel and filter paper, collecting the solution.
• Testing for proteins involves adding drops of Biuret solution to the food sample, a positive test will show a colour change from blue to violet / purple.
• The shape of a protein determines its function, for example, enzymes have a specifically shaped active site - where a specific substrate molecule fits in order for a reaction to take place.
• Testing for glucose involves adding Benedict’s solution to the sample solution in a test tube, heating in a boiling water bath for 5 minutes, taking the test tube out of the water bath and observing the colour, a positive test will show a colour change from blue to orange / brick red.
• Different proteins have different amino acid sequences resulting in them being different shapes.
• Antibodies are proteins produced by certain types of white blood cells that attach to antigens on the surface of pathogens, the shape of the antibody must match the shape of the antigen so that it can attach to it and signal it for destruction.
• Testing for lipids involves mixing the food sample with 4cm^3 of ethanol and shaking, allowing time for the sample to dissolve in the ethanol, straining the ethanol solution into another test tube, adding the ethanol solution to an equal volume of cold distilled water, a positive test will show a cloudy emulsion forming.
• Testing for starch involves adding drops of iodine solution to the food sample, a positive test will show a colour change from orange-brown to blue-black.