Biological significance of proteins:
a) Structural component of cells: Some protein serve as structural materials or as important component of extracellular fluid.
b) Food stuffs: To some extent, particularly in diabetic conditions proteins undergo gluconeogenesis and are used in cells as food stuffs after getting converted into glucose and glycogen.
c) Biocatalysts: The most striking characteristic feature of protein is their ability to function within living cells as reaction catalyzing enzymes. Enzymes usually enhance reaction rates by at least a million fold. These catalyst vary greatly in biological activity and properties but have in common the fact that they are all proteins of all kind or another. It has been estimated that about 90% of the total protein within a cell is actually enzyme protein. Life depends on enzymatic acceleration of reactions and living, there fore, means dependence on enzymatic functional proteins. Thus protein play the unique role of determining the pattern of chemical transformation in biological systems.
d) Hormones: Hormones from pancreatic islets of langerhans, Pitutary, Parathyroids and Gastro-intestinal mucosa are of peptide nature. Likewise, hormones from the thyroid and Adrenal Medulla are derivatives of amino acid tyrosine.
e) Oxygen carriers: Haemoglobin, the respiratory pigment of animals, is a conjugated protein composed of colorless basic protein, the globin, and ferroprotoporphyrin or haem. It has a unique ability to bind Oxygen in a loose and easily reversible combination. Myoglobin, a related protein, transports oxygen in muscle.
Cytochromes, the electron transfer agents, are basic proteins with an iron containing group derived from protoporphyrin.
f) Protection against diseases: Immunoglobulins of the blood plasma in mammals and other animals acts as antibodies that nuetralize the harmful effects of such foreign agents as viruses, bacteria and cell from other organisms. They also form basis of blood types.
g) Growth and repair: Proteins occupy a key position in general body growth and in the repair of water and tear of the cells and body as whole. During metabolic activities, tissue protein breakdown, and these damaged tissues are repaired with the help of amino acids.
h) Formation of Rhodopsin: The visual purple, rhodopsin is made up of retinene, an aldehyde derivative of vitamin A and a protein opsin.
i) Synthesis of Melanin: Melanin, the pigment of skin, hair and choroid layer of eye is derived from the amino acid tyrosine.
j) Urea formation: In ureotelic animals, the amino acids ornithine, citrulline and arginine participate in the formation of urea by a cyclic process.