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What would happen if in a gene encoding a polypeptide of 50 amino acids, 25th codon (UAU) is mutated to UAA?

1. A polypeptide of 25 amino acids will be formed
2. A polypeptide of 24 amino acids will be formed
3. Two polypeptides of 24 and 25 amino acids will be formed
4. A polypeptide of 49 amino acids will be formed

Correct answer: A polypeptide of 25 amino acids will be formed

Solution

UAU normally codes for tyrosine, but UAA is a stop codon. Translation will terminate when the ribosome reaches this new stop at the 25th codon, so the first 25 amino acids are produced and the rest of the polypeptide is not made.

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