Question

Protein structure is stabilized by different types of bonds.
Which of these best describes the types of bonds that stablize each level of protein structure?

• A. Primary-peptide bonds, Secondary-hydrogen bonds, Tertiary-disulfide bridges, Van der Waals interactions and ionic bonds.
• B. Primary-hydrogen bonds, Secondary-covalent bonds, Tertiary-ionic bonds.
• C. Primary-covalent bonds, Secondary-disulfide bridges, Tertiary-hydrogen bonds.
• D. Primary-hydrogen bonds, Secondary-peptide bonds, Tertiary-disulfide bridges, Van der Waals interactions and ionic bonds.
• E. Primary-peptide bonds, Secondary-covalent bonds. Tertiary-Van der Waals interactions and ionic bonds.

Answer 1

The correct option is A Primary-peptide bonds, Secondary-hydrogen bonds, Tertiary-disulfide bridges, Van der Waals interactions and ionic bonds.

There are four structural levels in proteins:

1. Primary structure: The number and sequence elucidated of amino acids in the polypeptide chain constitute the primary structure. The amino acids are linked with each other by peptide bond only.

2. Secondary structure: Long polypeptide chains fold or coil to form secondary structure. These secondary structures are produced and maintained by hydrogen bonding, Two types of secondary structures are:

(i) α helix- In this, the chain is coiled spirally, generally in the right handed manner. The helix is stabilised by Hydrogen bond between carboxylic acid of one amino acid and amino group of next fourth amino acid.

(ii) β pleated sheets- In this, two or more chains are joined together by intermolecular bond, Hydrogen bond.

3. Tertiary structure: The polypeptide chain may undergo coiling and folding to produce the tertiary structure. These structures are stabilised by the several types of bonds namely hydrogen bond, ionic bond, van der waal's interaction, covalent bond (disulphide bridges) and hydrophobic bond.

4. Quaternary structure: Protein is said to be in quaternary structure if they consist of two or more polypeptide chains united by the forces other than covalent bond. The forces which stabilise these structures are hydrogen bond and electrostatic bond.

So, the correct answer is 'Primary-peptide bonds, Secondary-hydrogen bonds, Tertiary-disulfide bridges, Van der Waals interactions and ionic bonds'.