Question

RNA and DNA are chiral molecules, their chirality is due to:
(A) D-sugar component
(B) L-sugar component
(C) Chiral bases
(D) Chiral phosphate ester units

Answer 1

Hint: If a molecule cannot be superimposed on its mirror image by any combination of rotations or translations then the molecule is said to be chiral. A chiral molecule has two stereoisomers that are mirror images of each other. The isomers are known as enantiomers.

Complete step by step solution:We know that RNA is ribonucleic acid. RNA contains a ribose sugar, a base and a phosphate group.
We know that DNA is deoxy ribonucleic acid. DNA contains a deoxyribose sugar, a base and a phosphate group.
The structures of ribose and deoxyribose sugars are as follows:

When the sugar molecule is drawn in Fischer projection and the most oxidised carbon atom is at the top and the hydroxyl $\left( { - {\text{OH}}} \right)$ on the bottom chiral centre points to the right side then it is known as D-sugar.
From the structures of ribose and deoxyribose sugars we can see that the most oxidised carbon atom is at the top and the hydroxyl $\left( { - {\text{OH}}} \right)$ on the bottom chiral centre points to the right side.
Thus, both the ribose and deoxyribose sugars are D-sugars.
We know that if a molecule cannot be superimposed on its mirror image by any combination of rotations or translations then the molecule is said to be chiral. Thus, the RNA and DNA molecules are chiral because of the sugar molecules.
Thus, RNA and DNA are chiral molecules, their chirality is due to D-sugar components.

Thus, the correct option is (A) D-sugar component.

Note: When the sugar molecule is drawn in Fischer projection and the most oxidised carbon atom is at the top and the hydroxyl $\left( { - {\text{OH}}} \right)$ on the bottom chiral centre points to the left side then it is known as L-sugar.