CBSE Class 12 Chemistry Notes: Biomolecules – Classification of Proteins According to Composition

(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.

Examples are:

Egg (albumin); Serum (globulins); Wheat (Glutelin); Rice (Coryzenin)

Conjugated proteins

(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.

Example:

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.

Example:

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:

Examples:

Albumin (egg)

Classification According to functions

The functional classification includes following groups.

Structural proteins

These are the fibrous proteins such as collogen (skin, cartilage & bones) which hold living system together.

Blood proteins

(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.

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