Both human DNA and RNA are chiral molecules. The chirality in DNA and RNA arises due to the presence of

We need to identify what causes chirality in DNA and RNA molecules.

Key Concept: Chirality in Nucleic Acids

Both DNA and RNA are chiral molecules. The chirality in nucleic acids arises from their sugar components:

- DNA contains 2-deoxyribose (a D-sugar)

- RNA contains ribose (a D-sugar)

These sugars have multiple chiral centers (asymmetric carbon atoms). In biological systems, nucleic acids exclusively use the D-configuration of these sugars. The D-sugar has specific spatial arrangements at each chiral carbon, making the entire nucleic acid molecule chiral.

Why not the other options?

- L-sugar component (Option 1): Biological nucleic acids use D-sugars, not L-sugars. L-nucleic acids do not occur naturally.

- Chiral phosphate unit (Option 2): The phosphate group itself ($$PO_4^{3-}$$) is achiral (tetrahedral with identical oxygen atoms). While the phosphodiester linkage can create a chiral center at phosphorus in some cases, the primary source of chirality is the sugar.

- Base unit (Option 4): The nitrogenous bases (A, T, G, C, U) are planar aromatic molecules that are achiral by themselves.

The correct answer is Option 3: D-sugar component.