Hormone X activates the cAMP second messenger system in its target cells. The greatest response by a target cell would come from ________.
A) applying a molecule of hormone X to the extracellular fluid surrounding the cell
B) injecting a molecule of hormone X into the cytoplasm of the cell
C) applying a molecule of cAMP to the extracellular fluid surrounding the cell
D) injecting a molecule of activated, cAMP-dependent protein kinase into the cytoplasm of the cell

Question

Quizplus · Accepted Answer

Hormone X activates the cAMP second messenger system in its target cells by binding to a receptor on the cell surface which then activates the production of cAMP inside the cell. Therefore, applying a molecule of hormone X to the extracellular fluid surrounding the cell would lead to the greatest response by a target cell. Injecting hormone X into the cytoplasm of the cell would not necessarily activate the cAMP system. Applying cAMP to the extracellular fluid surrounding the cell would not be effective unless the hormone X has already activated the cAMP system. Injecting activated, cAMP-dependent protein kinase into the cytoplasm of the cell would not necessarily activate the cAMP system unless there is an abundance of cAMP already present inside the cell.

Hormone X Activates the CAMP Second Messenger System in Its