( c) Tertiary structure The folding and superimposition of polypeptide chains forms a compact globular shape, termed as tertiary structure. It is stabilised by covalent, ionic, hydrogen and disulphide bonds.
The precise arrangement constitutes the quaternary structure.
Classification on the Basis of Hydrolysis Products
( i) Simple These yield only a-amino acids upon hydrolysis. e. g., albumin.
( ii) Conjugated proteins These yield α-amino acids and non-protein part, called prosthetic group.
Protein Nucleoproteins
Prosthetic group
Nucleic acid Phospho proteins Phosphoric acid Glycoproteins Metalioproteins
Carbohydrates Metals
Lipoproteins
Lipids
( iii) Derived proteins These are obtained by partial hydrolysis of simple or conjugated proteins.
Proteins → Proteoses → Peptones → Polypeptides
Classification on the Basis Functions
1. |
Structural proteins Fibrous proteins |
2. |
Enzymes Serve as biological catalyst e. g., pepsin, trypsin etc. |
3. |
Hormones Insulin |
4. |
Contractile proteins Found in muscles, e. g., myosin, actin. |