The purine base found in RNA and DNA is?

Appeared in: DSSSB - 28 August 2019 (Shift-1)

Explanation

Nucleic acids (DNA and RNA) are composed of nucleotides, which contain a nitrogenous base.
These bases are classified as purines (Adenine and Guanine) and pyrimidines (Cytosine, Thymine, and Uracil).
Adenine is a purine base that is a fundamental component of both DNA and RNA, making it the correct answer.

Option A: Myoglobin is an iron- and oxygen-binding protein located in muscle tissue. It has no structural role in nucleic acids like DNA or RNA.
Option C: Thymine is a pyrimidine, not a purine. Furthermore, it is found exclusively in DNA, not in both DNA and RNA.
Option D: Uracil is a pyrimidine, not a purine. It is found exclusively in RNA, where it replaces thymine.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Composition of Nucleic Acids (DNA & RNA) as background academic context rather than a clinical decision trigger.
A solid understanding of nucleic acid bases is foundational for genetics, molecular biology, and pharmacology.
Many antiviral (e.g., Acyclovir, Zidovudine) and anticancer (e.g., 5-Fluorouracil) drugs are analogs of purines or pyrimidines. They work by interfering with DNA or RNA synthesis in pathogens or cancer cells.
Genetic disorders like Lesch-Nyhan syndrome are caused by defects in purine metabolism, leading to an overproduction of uric acid.

How to Approach the Question

First, identify the key terms in the question: 'purine base', 'RNA', and 'DNA'.
Recall the two classes of nitrogenous bases: purines and pyrimidines. A helpful mnemonic is 'Pure As Gold' (Purines = Adenine, Guanine), which have two rings.
Recall the specific base composition for DNA (A, G, C, T) and RNA (A, G, C, U). Note that Thymine in DNA is replaced by Uracil in RNA.
Evaluate each option against the criteria from the question: Is it a purine? Is it in both DNA and RNA?
Myoglobin is a protein, so it's incorrect. Thymine and Uracil are pyrimidines and are specific to one type of nucleic acid.
Conclude that Adenine is the only option that is a purine and is present in both DNA and RNA.

Concept Tested & Keywords

Qo71kBHy0qsOeGSIKPk9qT

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 DSSSB - 28 August 2019 (Shift-1)

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