Question

Which of the following statements describes a nonsense mutation?

O
A. A single base in either DNA or mRNA is replaced with the wrong
base but codes for the same amino acid.
O
B. A single base in either DNA or mRNA is replaced with the wrong
base, producing a stop codon.
O
C. A single codon is replaced with a different codon, causing the
wrong amino acid to attach to the chain.
O
D. A single base in either DNA or mRNA is deleted or inserted,
causing protein synthesis to stop early.

Answer 1

Answer: The correct answer is option B.

Step-by-step explanation:

A point-nonsense mutation is type of mutation in which amino acid coding codon is converted into a stop codon.

Due to the stop codon protein translation terminates prematurely. Consequently, a truncated peptide chain is formed.

For example, at DNA level conversion of TTC into ATC results in formation of UAG in mRNA instead of AAG.

AAG codes for lysine whereas UAG is a stop codon.

Option D is incorrect as nonsense mutation is a type of point mutation, not a deletion or insertion.

Answer 2

D

Step-by-step explanation:

Premature termination of the translation results in an altered protein especially depending on where the point nonsense mutation occurs. The higher up the mutation the more lethal the mutation because an incomplete protein causes it to lose functionality. There are 3 stop codons; UAA, UGA UAG and normally occur after the complete translation of a full polypeptide that can fold into a functional protein.