Apentix/AP Biology/Unit 2: Cell Structure and Function/Question
AP Biologyhardmcq1 pt

In adipocytes, GLUT4 glucose carriers wait inside intracellular vesicles; insulin signaling makes those vesicles fuse with the plasma membrane. Which outcome follows within minutes?

A.Insulin phosphorylates glucose directly, forcing it through the lipid bilayer unaided.
B.Carrier density at the cell surface jumps, accelerating glucose uptake without new protein synthesis.
C.Vesicle fusion destroys GLUT4 carriers, so uptake falls until translation builds replacements.
D.GLUT4 switches from passive carrier to ATP-powered pump once insulin arrives.

Explanation

Core Concept

Fusion relocates finished GLUT4 already sitting in vesicle membranes, sharply raising surface carrier numbers. When insulin withdraws, membrane regions are retrieved back into vesicles and uptake sinks toward baseline. Speed comes from redistribution of existing proteins rather than new synthesis.

Correct Answer

BCarrier density at the cell surface jumps, accelerating glucose uptake without new protein synthesis.

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