Which of the following nitrogenous base is not present in RNA?

Appeared in: CIP Ranchi 2023

Explanation

Thymine is a pyrimidine base that is a fundamental component of DNA.
In RNA, the pyrimidine base Uracil replaces Thymine.
The other three bases listed—Adenine, Guanine, and Cytosine—are present in both DNA and RNA.
This difference is a key distinction between the chemical composition of DNA and RNA.

Option A: Adenine is a purine base that is present in both RNA and DNA.
Option C: Cytosine is a pyrimidine base that is present in both RNA and DNA.
Option D: Guanine is a purine base that is present in both RNA and DNA.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Composition of Nitrogenous Bases in RNA as background academic context rather than a clinical decision trigger.
Understanding the difference between DNA and RNA bases is fundamental to molecular diagnostics. For example, tests for RNA viruses (like Influenza, HIV, or SARS-CoV-2) use reverse transcription to convert the viral RNA (containing U) into DNA (containing T) for analysis by PCR.
Many antiviral and anticancer drugs are analogs of these bases. For instance, 5-Fluorouracil is a chemotherapy drug that interferes with the synthesis of thymine, thereby inhibiting DNA replication in rapidly dividing cancer cells.
What if the question asked which base is unique to RNA? The answer would be Uracil, as it is found in RNA but not in DNA.

How to Approach the Question

First, identify the core of the question, which is asking to identify a component that is not part of RNA.
Recall the basic building blocks of nucleic acids, specifically the nitrogenous bases.
List the four bases found in RNA: Adenine (A), Guanine (G), Cytosine (C), and Uracil (U).
List the four bases found in DNA for comparison: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
Compare the list of RNA bases with the given options.
The option 'Thymine' is not in the list of RNA bases, making it the correct answer.

Concept Tested & Keywords

QfDjNboGidXF5eOh1XW45q

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 216-218

E6 Biochemistry U Satyanarayana— Part 1 (pp 26-420 of 840) p. 61-63

Practise the full CIP Ranchi 2023

Attempt every question from this paper in a timed mock, then review the full solution for each one.