Question 35

Question:

A researcher has discovered a rare and previously unknown autoimmune disease. CD8+ T cells isolated from patients are resistant to apoptosis and proliferate at a much higher rate than normal. Upon further study, the researcher discovers that these cells contain a mutation in a cell surface receptor. The mutation causes the receptor to become inactive. Western blotting shows that the mutant and wild-type receptors have the same molecular weight. What type of mutation do these patients carry?

Correct Answer: C.  Missense single-nucleotide mutation

The only mutation which would result in a protein of the same molecular weight is a missense mutation which causes a single amino acid substitution. This may cause a structural change in the receptor, making it inactive or unable to bind its ligand.

Deletion, nonsense, and frameshift mutations would all result in a shortened protein.

A splice site mutation causes an intron to be left during mRNA processing resulting in a longer protein (or a shorter protein if the intron contains a stop codon).