19. Which of the following mutagens is most likely to results in a single amino acid change in a gene product?
(1) Acridine orange (2) X-rays
(3) EMS (4) Ethidium bromide
EMS (Ethylmethane sulfonate) is the mutagen most likely to result in a single amino acid change in a gene product.
Option Analysis
Acridine orange intercalates into DNA during replication, promoting insertions or deletions of bases that cause frameshift mutations. These shifts alter the reading frame, leading to extensive changes in the amino acid sequence downstream rather than a single substitution.
X-rays produce ionizing radiation that generates free radicals and directly breaks DNA strands, often resulting in large deletions, chromosomal breaks, or double-strand breaks. Such damage typically causes major structural alterations or loss of genetic material, not precise single base changes.
EMS (Ethylmethane sulfonate) acts as an alkylating agent that primarily ethylates guanine bases, converting them to O6-ethylguanine. During replication, this mispairs with thymine, inducing G:C to A:T transitions that change a single codon, often resulting in one amino acid substitution known as a missense mutation.
Ethidium bromide functions as an intercalating agent similar to acridine orange, inserting between base pairs and causing frameshift mutations through base additions or deletions during replication. It disrupts the reading frame, producing widespread protein alterations instead of isolated amino acid changes.
Exam Relevance
This question tests understanding of mutagen specificity in CSIR NET Life Sciences genetics sections. Point mutations from alkylating agents like EMS contrast with frameshifts from intercalators or gross damage from radiation, emphasizing mutation types and their protein impacts.
