Cyclic AMP (cAMP), Ca²⁺, and IP₃ are examples of

Answer: Second messengers — small intracellular molecules that propagate signals Second messengers amplify and spread the signal received at the membrane, triggering many downstream responses.

A drug that inhibits cAMP phosphodiesterase would most directly cause:

Answer: Prolonged activation of protein kinase A Phosphodiesterase degrades cAMP to AMP, ending the signal. Inhibiting it allows cAMP levels to remain elevated, prolonging PKA activity.

The arrangement shown is most often called a:

Answer: Phosphorylation cascade that amplifies the signal Each activated kinase phosphorylates many downstream kinases, multiplying the signal at each step and producing strong amplification.

AP Biology · Topic 4.3

Signal Transduction Practice

Part of Cell Communication and Cell Cycle.(IST-3.C)

Practice questions

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Sample questions

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Sample 1difficulty 2/5
$Cyclic AMP (cAMP), Ca²⁺, and IP₃ are examples of$
- A
  $Membrane receptors — transmembrane proteins that detect external chemical signals$
- B
  $First messengers — extracellular signaling molecules that bind to surface receptors$
- C
  $Second messengers — small intracellular molecules that propagate signals$
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- D
  $Adapter proteins — scaffolding molecules that organize relay components into pathways$
Why
$Second messengers amplify and spread the signal received at the membrane, triggering many downstream responses.$
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Sample 2difficulty 2/5
$Adenylyl cyclase converts ATP to the second messenger cAMP at the inner face of the plasma membrane.$
$A drug that inhibits cAMP phosphodiesterase would most directly cause:$
- A
  $Prolonged activation of protein kinase A$
  check_circle
- B
  $Loss of receptor binding$
- C
  $Decreased cAMP levels$
- D
  $Inhibition of adenylyl cyclase$
Why
$Phosphodiesterase degrades cAMP to AMP, ending the signal. Inhibiting it allows cAMP levels to remain elevated, prolonging PKA activity.$
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Sample 3difficulty 2/5
$The arrangement shown is most often called a:$
- A
  $Linear pathway with no amplification$
- B
  $Phosphorylation cascade that amplifies the signal$
  check_circle
- C
  $Positive feedback loop only$
- D
  $Negative feedback loop$
Why
$Each activated kinase phosphorylates many downstream kinases, multiplying the signal at each step and producing strong amplification.$
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Sample 4difficulty 2/5
$A signaling cascade with multiple kinase steps amplifies the signal because$
- A
  $Each kinase irreversibly converts itself into product, ensuring permanent activation of the response$
- B
  $Each kinase activates only one downstream substrate, but the pathway is extremely fast at every stage$
- C
  $Each kinase phosphorylates many target molecules, multiplying the response at each step$
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- D
  $Each kinase moves into the nucleus directly, where it acts as a transcription factor at every step$
Why
$A few activated receptors \to many activated kinases \to many more phosphorylated targets. Tiny signals can produce massive responses.$
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Sample 5difficulty 3/5
$Many signaling pathways release Ca²⁺ from the endoplasmic reticulum via$
- A
  $ATP synthase complexes$
- B
  $IP₃-gated calcium channels$
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- C
  $Aquaporin water channels$
- D
  $Voltage-gated sodium channels$
Why
$PLC cleaves PIP₂ \to DAG + IP₃. IP₃ binds and opens ER channels, releasing Ca²⁺ into the cytosol as a second messenger.$
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