| Proteins are fundamental structural compounds of the cell and are
made up of amino acids. They are mostly distributed in the muscle tissue and the rest is
distributed in the soft tissue, bone, teeth, blood and other body fluids. They are complex
organic compounds consisting of carbon, hydrogen, oxygen and nitrogen. Proteins are made
up of chains of amino acids joined together by peptide bonds. Proteins can be classified
according to their physical, chemical and nutritional properties.
- Classification according to physical properties;
Fibrous proteins: those that contain long, polypeptide chains bound together in a more
or less parallel fashion to form linear shape. E.g. keratin in hair.
Globular proteins: are proteins in which the chain of amino acids are coiled and
tightly packed together in a round, oval shape. E.g. casein.
- Classification according to chemical properties:
Simple proteins: are those proteins, which on hydrolysis yield only amino acids. E.g.
albumin
Conjugated protein: are composed of simple protein combined with a non-protein molecule
(prosthetic group). E.g. lipoprotein (fats and proteins)
- Classification according to nutritional properties:
Essential amino acids: are those which cannot be synthesised by the body and have to be
supplied in the diet.
Non essential amino acids: are those which can be synthesized in the body and need not
be supplied in the diet.
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