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 spectometry. 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 peaks suggests a small modification of the protein, and phosphorylation is a common post-translational modification that can cause a slight shift in the mass of the protein. The hormone likely triggered a signaling cascade that led to phosphorylation of the receptor protein. mRNA editing, alternative exon usage, and proteolytic processing would result in more significant changes in the amino acid sequence or size of the protein.

A Population of Cells Is Treated with a Polypeptide Hormone