Question

A research team discovered that a novel hormone X stimulates an enzyme that hydrolyzes proteins in the small intestine. However, when hormone X was added to a test-tube mixture containing the enzyme and proteins, no breakdown occurred.
Required:
a. Why is this the case?
b. Name ONE signal transduction pathway that hormone X is using to transfuse its signal. (write all the steps and intermediates)

Answer 1

Answer:

a. It is a hormone that acts upstream in the signaling pathway (i.e., acting as a ligand by binding to cell receptors)

b. Dopamine-mediated pathways  

Explanation:

It is well known that many cellular transduction pathways are activated via binding of signaling molecules (ligands) to receptors capable of triggering signaling cascades into the cell. For example, dopamine is a signaling hormone (neurotransmitter) involved in diverse brain processes (i.e., motor control, emotional response, etc). It is a neurotransmitter that binds to dopamine receptors and then stimulates the enzyme adenylate cyclase in a process that subsequently activates the production of the second messenger cyclic adenosine monophosphate (cAMP). Finally, cAMP acts as an intracellular signal transductor that play roles in many biological processes by transferring into the cell the effects of dopamine.