Question

Assertion: All proteinecous enzymes have a three-dimensional structure.
Reason: The secondary structure of protein is according to amino acid present inside the polypeptides.

• A. If both assertion and reason are true and reason is the correct explanation of assertion.
• B. If both assertion and reason are true but reason is not the correct explanation of assertion.
• C. If assertion is true but reason is false.
• D. If both assertion and reason are false.

Answer 1

Answer: (B)

The secondary structure of proteins is the development of new stearic relationships of amino acids present in the linear sequence inside the polypeptides. Some of the new relationship are of regular nature and give periodicity to the structure. There are three types of secondary structures - $\alpha$-helix, $\beta$-pleated and collagen helix. They are held in a particular structure due hydrogen bonds between oxygen of carboxylic group (-CO group) of one amino acid residue and >NH group of another amino acid. The protein enzymes have active sites which are capable of attracting and holding particular substrate molecules by is specific charge, size and shape so as to allow the chemical change. An active site consists of a few amino acids and their side groups which are brought together in a particular fashion due to secondary and tertiary folding of a protein molecule and its association with the cofactor, if any. Tertiary structure is bending and folding of various types to form spheres, rods or fibres. It further brings new stearic relationships of amino acids specially those which are far apart in the linear sequence. Tertiary structure is stabilized by several types of bonds— hydrogen bonds, ionic bonds, van der Waal's interactions, covalent bonds, hydrophobic bonds. Tertiary structure gives the protein a three dimensional conformation.