Apentix/AP Biology/Unit 1: Chemistry of Life/Question
AP Biologymediummcq1 pt

Many regulatory proteins switch their activity when an enzyme attaches a single phosphate group to one of their amino acid side chains. Why does this small chemical change exert such a large effect?

A.The phosphate burns away part of the protein, shortening its chain.
B.The attached phosphate converts the protein into a membrane channel.
C.The phosphate adds multiple negative charges that attract new partners and repel old contacts, reshaping the protein.
D.The phosphate raises the pH inside the cell and thereby denatures competing enzymes.

Explanation

Core Concept

A phosphate group carries two ionized negative charges at cellular pH, a dramatic local change for a protein surface. Those charges form attractions with positive patches elsewhere on the protein or on other molecules, pulling new shapes and assemblies into place while disrupting interactions that depended on the unmodified side chain. Conformation and binding partners therefore shift wholesale in response to one small covalent edit. Cells exploit this controllable switch throughout signaling cascades, and enzymes remove the phosphate to reset the system.

Correct Answer

CThe phosphate adds multiple negative charges that attract new partners and repel old contacts, reshaping the protein.

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