Question

Suppose the normal protein made from a gene has exactly 100 amino acids. A mutated version of this gene produces a protein only 20 amino acids long. Furthermore, the sequence of amino acids is the same for the first 6 amino acids, but completely different after that point. What kind(s) of mutation could cause this?

a) Frameshift mutation
b) Nonsense mutation
c) Missense mutation
d) Silent mutation

Answer 1

A nonsense mutation is most likely responsible for the dramatically shorter protein sequence, as it introduces a premature stop codon, truncating the normal protein after just 20 amino acids with a change after the sixth amino acid.

Step-by-step explanation:

In the context of the described scenario where a gene mutation results in a protein that is dramatically shorter and has a different amino acid sequence after a certain point, we can analyze the possible mutations. A frameshift mutation occurs due to an insertion or deletion, causing a shift in the reading frame of the genetic sequence which typically creates an entirely different sequence of amino acids. This often leads to non-functional proteins due to premature stop codons or extensive misfolding. A nonsense mutation changes an amino acid codon to a stop codon, terminating translation prematurely, which seems most relevant to the described situation. In contrast, a missense mutation changes a single amino acid to another, which would not typically create a much shorter protein. Lastly, a silent mutation does not change the amino acid sequence at all because it occurs in a region of redundancy in the genetic code.

The scenario described - a protein truncated to 20 amino acids that begins with 6 amino acids identical to the normal protein - suggests a nonsense mutation has occurred. This is due to the abrupt termination of the normal sequence after a certain point, leading to a much shorter protein.