The difference between RNA and DNA is because of:

Question

Accepted Answer

The correct option is 1: Sugar and base

The fundamental difference between Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA) lies in the structure of two of their three constituent components: the sugar and the base. Regarding the sugar, DNA contains **deoxyribose**, a pentose sugar that is 'de-oxygenated' because it lacks a hydroxyl (-OH) group at the 2' carbon position of the sugar ring. RNA, however, contains **ribose**, which possesses this hydroxyl group at the 2' carbon. This seemingly small chemical distinction makes DNA much more chemically stable and less susceptible to degradation, perfectly suiting its role as the long-term archive for genetic information. In terms of the nitrogenous bases, both nucleic acids share Adenine (A), Guanine (G), and Cytosine (C), but they differ in the fourth base. DNA exclusively contains **Thymine (T)**, while RNA contains **Uracil (U)** in place of Thymine. Because both the sugar and a critical nitrogenous base are unique to each molecule, the combination "Sugar and base" is the only correct and complete descriptor of their structural differences.

The incorrect option is 2: Sugar and phosphate

This option is incorrect because the phosphate group is chemically identical in both DNA and RNA and therefore does not contribute to the difference between them. The phosphate group is what forms the crucial phosphodiester bonds, which create the sugar-phosphate backbone of the nucleic acid polymer. Since the phosphate moiety is structurally and functionally the same in both molecules, it cannot be used to distinguish one from the other. Although the sugar component is correctly identified as a difference, its pairing with the non-differentiating phosphate group makes the entire option inaccurate as a complete description of the structural differences.

The incorrect option is 3: Only sugar

This option is an incomplete answer, as the difference between DNA and RNA is not limited solely to the sugar component. While the substitution of deoxyribose in DNA with ribose in RNA is certainly a key distinction, the nitrogenous bases also differ. Specifically, the base Thymine is found in DNA, while Uracil is found in RNA. Therefore, stating that *only* the sugar is responsible for the difference overlooks the unique base composition of each molecule. For a multiple-choice question asking for the difference, the most complete and accurate answer must include both of the variable components.

The incorrect option is 4: Base and phosphate

This option is incorrect for the same reason as option 2: the phosphate group is not a distinguishing feature between DNA and RNA. The structure and chemical role of the phosphate group are the same in both molecules. Although the nitrogenous base is correctly identified as a point of difference (Thymine vs. Uracil), the inclusion of the phosphate group, which is shared by both, invalidates this option as a complete and correct description of the structural differences between the two nucleic acids.