Differentiate between globular and fibrous proteins.

Explanation

(i) Fibrous proteins : These proteins consist of linear thread like molecules which tend to lie side by side (parallel) to form fibres. The polypeptide chains in them are held together usually at many points by hydrogen bond and some disulphide bonds. As a result intermolecular forces of attraction are very stron and hence fibrous proteins are insoluble in water. Further, these proteins are stable to moderate changes in temperature and pH. Fibrous proteins serve as the chief structural material of animal tissues. For example, keratin in skin, hair, nails and wool, collagen in tendons, fibrosis in silk and myosin in muscles.
(ii) Globular proteins : The polypeptide chain in these proteins is folded ground itself in such a way so as to give the entire protein molecule an almost spheroidal shape. the folding takes place in such a manner that hydrophobic (non-polar) parts are pused inwards and hydrophilic (polar) parts are pushed outwards. As a result, water molecules interact stronly with the polar groups and hence globular protein are water molecular interact stronly with the polar groups and hence globular protein are water soluble. As compared to fibrous proteins, these are very sensitive to small changes of temperature and pH. This class of proteins include all enzymes, many hormones such as insulin from pancrea, thyroglobulin from thyroid gland etc.