Multiple Choice
Which of the following is true about water-soluble hormones?
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16. The Endocrine System
Membrane Bound Receptors and Secondary Messengers
Problem 20
Textbook Question
How would blocking the activity of phosphodiesterase (PDE) affect a cell that responds to hormonal stimulation by the cAMP second messenger system?
Verified step by step guidance1
Step 1: Understand the role of phosphodiesterase (PDE) in the cAMP second messenger system. PDE is an enzyme that breaks down cyclic AMP (cAMP) into AMP, thereby reducing the intracellular concentration of cAMP and terminating the signal.
Step 2: Recall that cAMP acts as a second messenger that activates protein kinase A (PKA), which then phosphorylates target proteins to elicit a cellular response to hormonal stimulation.
Step 3: Consider what happens if PDE activity is blocked. Since PDE normally degrades cAMP, blocking PDE will prevent cAMP breakdown, leading to an accumulation of cAMP inside the cell.
Step 4: Analyze the consequence of increased cAMP levels. Elevated cAMP will prolong and amplify the activation of PKA, resulting in a stronger and longer-lasting cellular response to the hormone.
Step 5: Summarize that blocking PDE enhances the hormonal signal by maintaining higher cAMP levels, which sustains the activation of downstream signaling pathways and cellular effects.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Phosphodiesterase (PDE) Function
Phosphodiesterase enzymes break down cyclic AMP (cAMP) into AMP, terminating the cAMP signaling. By degrading cAMP, PDE regulates the intensity and duration of the signal inside the cell, ensuring that the response to hormonal stimulation is properly controlled.
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Functional Groups
cAMP Second Messenger System
The cAMP second messenger system transduces extracellular hormonal signals into intracellular actions. When a hormone binds to its receptor, it activates adenylate cyclase to produce cAMP, which then activates protein kinase A (PKA) to trigger downstream cellular responses.
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Effect of PDE Inhibition on Cellular Signaling
Blocking PDE activity prevents cAMP breakdown, leading to elevated and prolonged cAMP levels. This enhances and extends the hormonal signal, potentially amplifying cellular responses such as enzyme activation, gene expression, or metabolic changes.
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