Which of the following attractive forces are responsible for the tertiary structure of proteins?
1. (i) ionic bonds
(ii) hydrogen bonds
(iii) van der Waals forces
(iv) disulphide linkages

Options

A. (ii) only
B. (ii) and (iv)
C. (i),(ii),(iii) and (iv)
D. (ii),(iii), and (iv)

Answer

C

Explanation

The unique three-dimensional shape of a protein is the result of the intermolecular forces of attraction that cause bending and coliling in the helical coil. These forces are a function of the nature of the `A A` side chains within the molecule.
Globular proteins have their nonpolar `R` group pointing to the interior (the hydrophobic or non-aqueous region) and their polar side chains projecting toward the aqueous environment, somewhat like a micelle. They are some what water soluble.
Fibrous proteins are insoluble in water. Their polypeptide chains are held together by interchain `H` - bonds
The following are the attractive forces responsible for the tertiary structure:
(i) Inoic bonding between `COO^(-)` and `overset(+)NH_(3)` at different sites
(ii) `H -` bonding mainly between side-chain `NH_(2)` and `COOH`, aslo involving `OH`, (e.g., of serine) and `N - H` of tryptophane
Weakly hydrophobic van der waals attractive forces engendered by side-chain `R` groups
(iv) Disulphide cross linkage between loops of the polypetides chain.
The same kind of attractive and prepulsive forces responsible for the tertiary structure operate to held together and stablized the subunits of the quaternary structure.