Question

Which of the following steps would be prevented if adenylate cyclase was nonfunctional in the target cell of a water-soluble hormone?

A. Activation of a G protein
B. Formation of DAG and IP₃

Answer 1

The non-functionality of adenylate cyclase would prevent the formation of cAMP and, as a result, inhibit the activation of protein kinases and the phosphorylation cascade that normally follows water-soluble hormone binding.

Step-by-step explanation:

If adenylate cyclase was nonfunctional in the target cell of a water-soluble hormone, the formation of cyclic AMP (cAMP) would be prevented. When a water-soluble hormone binds to its receptor on the cell membrane, an associated G protein is typically activated. This activated G protein then stimulates adenylate cyclase to convert ATP into cAMP, which serves as a second messenger. cAMP then activates protein kinases, leading to a cascade of cellular responses. Therefore, if adenylate cyclase is not functional, the signal cannot be transduced and the subsequent activation of protein kinases and cellular responses would be inhibited.

Steps affected by nonfunctional adenylate cyclase:

• cAMP synthesis from ATP, catalyzed by adenylate cyclase, is blocked.
• Activation of protein kinases that require cAMP is prevented.
• Phosphorylation cascade initiated by protein kinases does not occur, stopping the cellular response.