Final answer:
All options (a, b, c) regarding hormone analogs and their ability to bind and influence receptors are correct. Hormone antagonists can block the signaling pathways of hormones such as testosterone. Hormone action can be direct, involving intracellular receptors, or indirect through second messenger systems like cAMP.
Step-by-step explanation:
Hormone analogs can bind receptors with varying outcomes: they might have a higher affinity than the natural hormone, they could either activate or block signaling through the receptor. Therefore, all of the options listed (a, b, c) are correct, making the answer d. All of the answers are correct.
For instance, a new antagonist molecule that blocks plasma membrane receptors will prevent testosterone from binding to its receptor and consequently block the signal it would otherwise initiate. This antagonist essentially serves as a form of inhibitor for the hormone's usual pathway.
If a chemical serves as an inhibitor of the enzyme adenylyl cyclase, it would block the synthesis of cAMP, which is a crucial step in certain G-protein signaling pathways initiated by hormones. Hormones like insulin utilize receptors to induce cellular responses such as receptor down-regulation upon bonding and internalization by the cell.
It's important to understand that hormones can mediate changes in different ways. They may act directly on DNA by binding to intracellular hormone receptors, or indirectly by binding to cell surface receptors to initiate signaling pathways involving second messengers like cAMP. This discrepancy is often based on whether the hormone is lipid-soluble.