(A) Deaminating agent

(B) Alkylating agent

(C) Intercalating agent

(D) Base analogue

Ethidium bromide is a classic intercalating agent used in molecular biology labs. This article covers Q.48 on its mutagenic action with the correct answer and breakdowns of all options.

Correct Answer

The correct answer is (C) Intercalating agent.

Ethidium bromide (EtBr) features a flat, planar ring structure that slips between DNA base pairs, known as intercalation. This distorts the DNA helix, unwinds it, and disrupts replication, transcription, and repair, causing frameshift mutations.

Option Breakdowns

(A) Deaminating Agent

Deaminating agents like nitrous acid remove amino groups from bases (e.g., cytosine to uracil), leading to base mismatches.
Ethidium bromide does not deaminate; it physically inserts into DNA stacks instead.

(B) Alkylating Agent

Alkylating agents such as mustard gas add alkyl groups to DNA bases, causing cross-links or breaks.
EtBr lacks this chemical reactivity; its effect is structural insertion, not covalent modification.

(C) Intercalating Agent

EtBr intercalates between base pairs due to its phenanthridine ring, increasing DNA length by ~26% per molecule.
This interference induces mutations, explaining its use (and hazard) in DNA visualization via gel electrophoresis.

(D) Base Analogue

Base analogues like 5-bromouracil mimic nucleotides and pair erroneously during replication.
EtBr does not incorporate as a base; it binds externally between existing pairs.