Question

Both $\text{DNA}$ and $\text{RNA}$ are chiral molecules. The chirality in $\text{DNA}$ and $\text{RNA}$ arises due to the presence of :

• A. $\text{D}$-sugar component
• B. Phosphodiester linkage
• C. $\text{L}$-sugar component
• D. Nitrogenous bases

Hint:

The chirality of natural biopolymers (proteins, nucleic acids) stems from the chiral centers present in their primary building blocks (L-amino acids, D-sugars).

Answer 1

The Correct Option is A

The question asks about the source of chirality in DNA and RNA molecules. Let's examine each option and provide reasoning to determine the correct answer:

1. $\text{D}$-sugar component: D-sugars, specifically deoxyribose in DNA and ribose in RNA, are responsible for the chirality of these molecules. The sugars have a chiral center at the second carbon, which gives the entire sugar molecule, and consequently the nucleic acid, its chirality. Chirality is a property where a molecule cannot be superimposed on its mirror image, much like left and right hands. Therefore, this is indeed the correct source of chirality in DNA and RNA.
2. Phosphodiester linkage: The phosphodiester linkage is the bond between the phosphate group and the sugar in the backbone of DNA and RNA. This bond is not responsible for chirality, as it does not contain chiral centers like the sugar component does.
3. $\text{L}$-sugar component: DNA and RNA do not naturally incorporate L-sugars. Instead, they contain D-sugars, as previously mentioned. Thus, this option is incorrect.
4. Nitrogenous bases: These are the building blocks of the nucleic acids (adenine, guanine, cytosine, thymine, and uracil), but they do not contribute to the chirality of the DNA or RNA molecule itself. The chirality arises primarily from the sugar component in the backbone.

Conclusion: The chirality in both DNA and RNA is due to the presence of the D-sugar component, specifically the chiral carbon atoms in ribose and deoxyribose. Therefore, the correct answer is the D-sugar component.