ABSTRACT
Role of proteins Proteins are very versatile macromolecules involved in almost all biological processes. Proteins can provide the impetus (or act as catalysts) for chemical reactions to occur under physiological conditions. In many instances a protein can increase the rate of a reaction a million-fold. In this role proteins are referred to as enzymes (but not all biological catalysts are proteins). Protein molecules can act as the carriers of important small molecules or ions. For example, the protein hemoglobin transports a molecule of oxygen (Sections F3 and G2) in erythrocytes and iron is transported by proteins called transferrins in blood plasma (Section G2). Antibodies are proteins that recognize foreign agents such as bacteria, and group together to remove them. The mechanical properties of proteins in, for example, our skin, are due to the mechanical properties of a fibrous protein called collagen. Proteins are involved in the generation and transmission of impulses to nerve cells and they are involved in cell growth and differentiation. In the latter role the
proteins are highly specialized molecules called hormones (Section M3). An example of a hormone that is also a protein is insulin.
