Proteins

All proteins molecules contain carbon, hydrogen, oxygen and nitrogen. Some contain sulphur and phosphorus. An example of a protein is the hormone insulin C254H317O75N65S6. Proteins are made up of long chains of basic units called amino acids. There are twenty three amino acids, each of which has two functional groups: the carboxyl group (-COOH) and the amino group (-NH2). They two groups are attached to a central carbon atom to which two other groups are attached to a central carbon atom to which two other groups, a side chain (usually denoted by –R) and a hydrogen atom are bonded. The simplest amino acid is glycine others are alanine, aspartic acid and lysine. Protein synthesis is a condensation reaction involving joins with the carboxyl group of another amino acid. A molecule of water is produced in the process (condensation). A dipeptide is formed, joining the two amino acids together. A peptide bond links the amino acids. Polypeptide or protein is formed when many amino acids are linked by peptide bonds. Proteins differ in structure and function. They may be used in the formation of: • Protoplasm, the living substances in plants and animals • Enzymes • Hormones eg. Insulin • Skeletal muscles, cartilage, tendons • Keratin, the protein forming the hair, nails, horns and hooves of animals They may also be used as sources of energy when respired, especially in carnivores. In plants, proteins occur in high concentration in the seeds of legumes (for example cowpea, kidney bean, Soya bean and groundnut). Plant protein is termed second class protein. Animal protein (in meat), contains all the essential amino acids (those amino acids essential for building the proteins that the body needs, but cannot be manufactured in the body). Such proteins are called first class proteins. Proteins loose their structure and are denatured through the action of heat, strong acids and alkalis, and organic solvents. For example the protein, albumen, in egg becomes denatured and turns white and hard when boiled.