Proteins are very useful starting materials, for example animal hide protein is processed to make leather, and silk is manufactured by the silk worm. Scientific techniques, known as protein as protein engineering have been developed to used micro-organisms to produce proteins in bulk, this is done by making changes to the sequence of amino-acids. The result of this allows proteins to perform new and different tasks. This has a useful implication, as protein engineering is important in the diagnosis and treatment of severe medical conditions.
Proteins are crucial to all biological living processes, and play a wide range of functions, these include:
Enzyme Catalysis - here all biological systems are catalyzed by a specific enzyme, and hence can increase the rate of a reaction by a million fold. They have vast catalytic power. All known enzymes are proteins, and hence they play an important role in chemical transformations in biological systems.
Transport and Storage - specific proteins can transport small molecules and ions, such as oxygen in hemoglobin, which are found in erytrocytes, and myoglobin transports oxygen in muscle. Transferrin another protein carries iron around the body and is stored in the liver.
Coordinated motion - contraction of muscle is achieved by the sliding motion of proteins.
Mechanical support - collagen, a fibrous protein found in skin and bone provides high tensile strength, and hence a major component in muscle. Movement of chromosomes in mitosis and the repulsion of sperm flagella are all examples of coordinated muscle contraction in proteins.
Immune protection - Antibodies which are synthesized by an animal, are very specific proteins, and can therefore distinguish between self and nonself. A major type of antibody in blood plasma is immunoglobulin G. Antibodies combine with foreign substances known as antigens, these being bacteria, viruses, and cells from other organisms. Proteins, polysaccharides, and nucleic acids all make effective antigens.
Production and transmission of nerve impulses - receptor molecules are involved in the mediation of response stimuli by nerve cells. Acetylcholine is an example of a receptor molecule which can be triggered by small molecules, in this case the receptor is responsible for the transmission of nerve impulses at synapses, i.e. at junctions between nerve cells.
Growth control and differentiation - Controlled sequential expression of genetic information is crucial for cell growth and differentiation. Repressor proteins in bacteria are important in controlling the silence of specific segments of a DNA molecule in a cell. Growth factor proteins control growth and differentiation in higher organisms. For example the activities of different cells in multicellular organisms are controlled by hormones, many of them proteins such as insulin and thyroid stimulating hormones. Proteins are excellent sensors in all living cells, and hence control the flow of energy and matter.