Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
An element that is present in a nucleotide but not in a nucleoside is ________.
Options:
(A) carbon
(B) nitrogen
(C) oxygen
(D) phosphorous
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2024 Q.24)**
**1. Governing Concept**:
- **Topic**: Biochemistry & Nucleic Acid Chemistry
- Structural definitions:
- **Nucleoside** = Nitrogenous Base + Pentose Sugar (elements: C, H, O, N).
- **Nucleotide** = Nucleoside + Phosphate group ($\text{PO}_4^{3-}$) (elements: C, H, O, N, and **P**).
- Therefore, the chemical element uniquely present in a nucleotide but absent in a nucleoside is **phosphorus**.
**2. Option Analysis**:
- **Option (A) [carbon] is INCORRECT**: Present in both pentose sugar and nitrogenous base.
- **Option (B) [nitrogen] is INCORRECT**: Abundantly present in both purine and pyrimidine rings.
- **Option (C) [oxygen] is INCORRECT**: Present in ribose/deoxyribose sugars of both nucleosides and nucleotides.
- **Option (D) [phosphorous] is CORRECT**: Added as esterified phosphate to convert a nucleoside into a nucleotide.
**3. Final Answer**:
- **Correct Choice**: **D**
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