Q.24 An element that is present in a nucleotide but not in a nucleoside is ________.
(A) carbon
(B) nitrogen
(C) oxygen
(D) phosphorous
Nucleotides form the building blocks of DNA and RNA, differing from nucleosides by one key component. The correct answer to the query is phosphorous, as it appears exclusively in nucleotides.
Nucleoside vs Nucleotide Structures
Nucleosides consist of a nitrogenous base linked to a sugar molecule, either ribose or deoxyribose. Nucleotides extend this by adding one to three phosphate groups to the sugar’s 5′ carbon, introducing phosphorous from the phosphate (PO4).
This phosphate linkage enables polymerization into nucleic acids, absent in nucleosides. All options except phosphorous exist in both structures.
Correct Answer: (D) Phosphorous
Phosphorous defines nucleotides through the phosphate group, critical for energy transfer (ATP) and DNA/RNA backbone formation. Nucleosides lack this group, so no phosphorous appears in their elemental composition.
Option Explanations
| Option | Element | Present in Nucleoside? | Present in Nucleotide? | Explanation |
|---|---|---|---|---|
| (A) Carbon | C | Yes | Yes | Forms the sugar backbone (ribose/deoxyribose) in both. |
| (B) Nitrogen | N | Yes | Yes | Key component of nitrogenous bases (A, G, C, T/U) in both. |
| (C) Oxygen | O | Yes | Yes | Abundant in sugar hydroxyl groups and bases in both; extra in nucleotide phosphates. |
| (D) Phosphorous | P | No | Yes | Exclusive to nucleotide phosphate groups. |
