Hormone X activates the cAMP second messenger system in its target cells. The greatest response by a 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 cAMP into the cytoplasm of the cell.
E) 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, which means that it binds to a receptor on the cell surface and triggers the production of cAMP within the cell. Therefore, the greatest response by a cell would come from applying a molecule of hormone X to the extracellular fluid surrounding the cell, as this would result in the highest concentration of hormone X available to bind to cell surface receptors and activate the cAMP system. Injecting a molecule of hormone X into the cytoplasm of the cell or injecting a molecule of cAMP into the cytoplasm of the cell would not necessarily result in the same level of activation of the cAMP system as applying hormone X to the extracellular fluid. The injection of activated, cAMP-dependent protein kinase into the cytoplasm of the cell may activate downstream targets, but would not necessarily stimulate the production of more cAMP.

Hormone X Activates the CAMP Second Messenger System in Its