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Cyclic AMP signaling is terminated when cAMP is broken down into AMP. Which enzyme carries out this degradation?
AThe enzyme phosphodiesterase
BThe enzyme adenylyl cyclase
CA phosphatase acting on cAMP
DThe enzyme protein kinase A
Answer & Solution
Correct answer: A. The enzyme phosphodiesterase
1. Cyclic AMP is degraded into AMP by the enzyme phosphodiesterase.
2. Calcium signaling is separately reversed by calcium pumps located in the external and internal membranes of the cell.
3. Adenylyl cyclase instead synthesizes cAMP from ATP, the opposite reaction from the one that terminates the cAMP signal.
4. Protein kinase A is activated by cAMP rather than being the enzyme that degrades it.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 9 "Cell Communication", section Termination of the Signal Cascade_
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