Secrets of protiens

SECRETS OF PROTIENS

Introduction to Proteins:
Proteins are essential constituents of protoplasm. They differ from carbohydrates and lipids by always con­taining nitrogen and sometimes phosphorus and sulphur. Proteins contain: carbon-54%; hydrogen-7%; nitrogen-16%; oxygen-22%. Some may contain, sulphur-1%; while others, phosphorus-0.6%.
Proteins are among the most abundant organic molecules; in most living systems they make up 50 percent or more of the dry weight. Only plants, with their high cellulose content, are less than half protein. The protein molecule is built up by the union of a large number of amino acids. The amino acids should be considered as the units with which the protein molecule is composed.
It is to be specially noted that the term protein is applied only to the complex protein molecule responding to the characteristic tests of protein, e.g., copper-protein (biuret) test, etc., due to the presence of two or more peptide linkages whereas amino acids do not respond to the characteristic tests of protein; hence they are called one of the non-protein nitrogenous (NPN) constituents.
(a) Protein acts as a growth material for the organism,
(b) Structures of living materials are composed of different types of protein molecules,
(c) It also acts as a part of fuel of the organism,
(d) All the pituitary hormones, hypothalamic-releasing factors (R.F.), certain placental hormones, pancreatic hormones, etc., are proteins in nature,
(e) Similarly all enzymes are proteins in nature.
In general, fibrous proteins have a regular, repeated sequence of amino acids and so a regular, repetitious structure. An example is collagen, which makes up about one-third of all the protein in vertebrates. The basic collagen molecule is composed of three very long polymers of amino acids-about 1,000 amino acids per chain.
These three polymers, which are made up of repeating groups of amino acids, are held together by hydrogen bonds linking amino acids of different chains in a tight coil. The molecules can coil so tightly because every third amino acid is glycine, the smallest of the amino acids.
Collagen performs many functions in the body. Consider a cow. Tendons, which link muscle to bone, are made up of collagen fibers in parallel bundles; thus arranged, they are very strong but do not stretch. The cow’s hide, by contrast, is made up of collagen fibrils arranged in an interlacing network laid down in sheets.
Even its corneas-the transparent coverings of the eyeballs-are composed of collagen. Boiling in water disperses the polymers of collagen into shorter chains, which we know as gelatin. Other fibrous proteins include elastin, present in the elastic tissue of ligaments, silk, and keratin.