Q.13 A frameshift mutation is caused by ____.
(A) 5–Bromouracil
(B) Acridine
(C) Glutathione
(D) Hypoxanthine
A frameshift mutation is caused by (B) Acridine. This is the correct answer for the CSIR NET Life Sciences exam question, as acridine dyes intercalate into DNA and induce insertions or deletions that shift the reading frame.
What is a Frameshift Mutation?
A frameshift mutation occurs when nucleotides are inserted or deleted in a number not divisible by three, altering the codon reading frame during translation. This leads to a completely different amino acid sequence downstream, often producing a nonfunctional protein. Unlike point mutations, which substitute one base, frameshifts disrupt the entire genetic code triplet structure.
Option Analysis
-
(A) 5-Bromouracil: This base analog mimics thymine but can tautomerize to pair with guanine, causing transition mutations (e.g., A-T to G-C). It does not insert or delete bases, so it cannot cause frameshifts.
-
(B) Acridine: Acridine dyes (e.g., proflavin, acridines) are intercalating agents that slip between DNA base pairs, promoting addition or loss of single nucleotides during replication. This directly induces frameshift mutations.
-
(C) Glutathione: An antioxidant tripeptide that protects cells from oxidative damage; it has no mutagenic properties or role in DNA alterations.
-
(D) Hypoxanthine: A deaminated adenine derivative formed by nitrous acid or APOBEC enzymes, leading to base substitutions (transitions). It does not cause indels for frameshifts.
Introduction to Frameshift Mutation Caused by Acridine
In molecular biology, a frameshift mutation caused by acridine disrupts DNA reading frames through intercalation, making it a classic topic for CSIR NET aspirants. This SEO-optimized guide explains every option—acridine, 5-bromouracil, glutathione, hypoxanthine—with mechanisms, examples, and exam tips.
Mechanisms of Key Mutagens
Frameshift mutations arise from indels not in multiples of three, unlike substitutions from base analogs.
| Mutagen | Type | Mutation Caused | CSIR NET Relevance |
|---|---|---|---|
| Acridine | Intercalator | Frameshift (indels) | Correct answer; slips between bases |
| 5-Bromouracil | Base analog | Transitions (AT→GC) | Incorrect; tautomerizes to pair with G |
| Glutathione | Antioxidant | None | Irrelevant; no DNA interaction |
| Hypoxanthine | Deamination product | Transitions | Incorrect; base substitution only |
Exam Tips for CSIR NET
Focus on acridines for frameshifts vs. analogs like 5-bromouracil for transitions. Practice with examples: Acridine in T4 phage studies showed +1/-1 shifts. Master this for genetics sections.
