Functions, properties, sources and requirements of proteins

Functions of proteins

    The important functions of dietary proteins are
    i) To replace the daily loss of body proteins
    ii) To provide amino acids for the formation of tissue proteins during growth
    iii) To provide amino acids necessary for the formation of enzymes, blood proteins and certain hormones of protein nature and
    iv) To provide amino acids for growth of fetus in pregnancy and for the production of milk proteins during lactation.

    Amphoteric nature
    Like amino acids, proteins are amphoteric, that is, they act as both acids and bases. Since proteins have electric charges, they migrate in an electric field, the direction of migration depending on the net charge on the molecule. For each protein, there is a pH at which the positive and negative charges will be equal and protein will not move in an electric field. This pH is known as the isoelectric point of the protein.
    Each protein has a definite and characteristic solubility in a solution of known salt concentration and pH. Albumins are soluble in water. Globulins are soluble in neutral sodium chloride solutions but are almost insoluble in water.
    Colloidal nature of protein solutions
    Proteins have large molecular weights. Protein solutions are colloids. They do not pass through semi permeable membranes. This property of proteins is of great physiological importance

    Best sources: Meat, fish, poultry, eggs, milk and milk products
    Good sources: cereals and legumes
    Requirements - RDA
    Children g/day
    1-3 years - 16.7
    4-6 years - 20.1
    7-9 years - 29.5

    10-12 years - 39.9
    13-15 years - 54.3
    16-18 years - 61.5

    10-12 years - 40.4
    13-15 years - 51.9
    16-18 years - 55.5

    Adult man - 60
    Adult woman - 55.5
    Pregnant woman - 82.2
    Lactation - 77.9

Last modified: Thursday, 21 June 2012, 9:36 AM