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Second Messengers and Enzymes
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AP Biology
APB.217 Second Messengers and Enzymes
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A mutant cell has high cAMP before ligand addition and shows a response even without ligand. Adding a phosphodiesterase inhibitor makes cAMP even higher. Which defect best fits the observations?
A
A regulatory defect causing excessive cAMP production or reduced control upstream of cAMP breakdown
B
A target protein with no phosphorylation sites
C
A PKA catalytic site completely unable to transfer phosphate
D
A receptor that cannot bind ligand under any condition
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