A population of cells is treated with a polypeptide hormone that induces mitosis and the hormone's cell surface receptor is isolated after 15 minutes and subjected to fragmentation and mass spectrometry. Several of the peaks show a slight shift as compared to the same protein from cells not treated with the hormone. What is the most likely explanation of this phenomenon?
A) Phosphorylation of some amino acid residues.
B) mRNA editing resulting in a slightly different amino acid sequence.
C) Alternative exon usage.
D) Proteolytic processing.

Question

Quizplus · Accepted Answer

The slight shift in the mass of the hormone receptor protein peaks suggests the addition of a phosphate group to one or more amino acid residues. This is a common post-translational modification that occurs rapidly in response to hormonal signals and can modulate receptor activity.

A Population of Cells Is Treated with a Polypeptide Hormone