13. Which of the following statements about signal transduction pathways is correct?
(A) All signaling molecules can pass directly through the plasma membrane.
(B) Protein kinases in signaling pathways often amplify the cellular response.
(C) Receptor proteins always function as ion channels.
(D) Second messengers are membrane-bound proteins.
(E) Signal transduction terminates only when the ligand is degraded.

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統計: A(0), B(1), C(0), D(0), E(0) #3852867