The codons for the various amino acids are given below. Answer the question.
In the given RNA the nitrogenous base at position 2 of the fourth codon is replaced by G. What will be the effect on protein synthesis?
AUG GUU AGU UAA
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → No effect on protein synthesis
The fourth codon is UAA. Replacing its second base (A) by G gives UGA. Both UAA and UGA are stop codons, so translation still ends after the third amino acid and the polypeptide Met–Val–Ser is unchanged.
Option (1) Different protein is synthesised — Incorrect. The first three codons are untouched and the stop signal remains, so the same protein is made.
Option (2) Change in amino acid at position four — Incorrect. The fourth codon codes for no amino acid before or after the change.
Option (3) No effect on protein synthesis — Correct. The fourth codon is UAA, a stop codon. Replacing its second base with G gives UGA, which is also a stop codon, so the polypeptide still ends at the same place and protein synthesis is not affected.
Option (4) Transcription will not be initiated — Incorrect. Transcription is the copying of DNA into RNA; a change in the mRNA cannot stop it.