(i) Simple proteins are those which yield only α-amino acids upon hydrolysis.
(ii) Simple proteins are composed of chain of amino acid unit only joined by peptide linkage.
Egg (albumin); Serum (globulins); Wheat (Glutelin); Rice (Coryzenin)
(i) Conjugated proteins are those which yield α – amino acids plus a non protein material on hydrolysis.
(ii) The non protein material is called the prosthetic group.
Casein in milk (prosthetic group is phosphoric acid); Hemoglobin (prosthetic group is Nucleic acid); Chlolesterol (prosthetic group – lipid).
According to molecular shape, proteins are further classified into two types.
(A) Fibrous protein
(a) These are made up of polypeptide chain that are parallel to the axis & are held together by strong hydrogen and disulphide bonds.
(b) They can be stretched & contracted like thread.
(c) They are usually insoluble in water.
Keratin (hair, wool, silk & nails); Myosin (muscle)
(B) Globular Proteins
(a) These have more or less spherical shape (compact structure).
(b) α – amino helix are tightly held bonding; H – bonds, disulphide bridges, ionic or salt bridges:
Classification According to functions
The functional classification includes following groups.
These are the fibrous proteins such as collogen (skin, cartilage & bones) which hold living system together.
(i) The major proteins constituent of the blood are albumin hemoglobin & fibrinogen.
(ii) Their presence contribute to maintenance of osmotic pressure, oxygen transport system & blood coagulation respectively.