[Campbell Biology P.281] Based on Concept 11.3, which statement accurately distinguishes bet... | Practice Question
Based on Concept 11.3, which statement accurately distinguishes between a protein kinase and a second messenger in a signal transduction pathway?
A: A protein kinase amplifies the signal by adding phosphate groups, while a second messenger directly binds to and activates the receptor.
B: A protein kinase is typically a large protein that phosphorylates other proteins, whereas a second messenger is a small, nonprotein, water-soluble molecule or ion that diffuses rapidly.
C: Protein kinases are only involved in nuclear responses, while second messengers are only involved in cytoplasmic responses.
D: Both protein kinases and second messengers are always activated by G protein-coupled receptors.
Explanation
Protein kinases are enzymes, typically large proteins, that add phosphate groups to other proteins in phosphorylation cascades, thereby changing their activity. Second messengers, in contrast, are small, nonprotein, water-soluble molecules or ions like cAMP, Ca2+, DAG, IP3 that diffuse rapidly through the cytosol to broadcast signals.