Question

Which of these hormones uses cAMP as a second messenger? a. Testosterone b. Cortisol c. Insulin d. Epinephrine

Short answer

d. Epinephrine

Step-by-step solution

Understanding Second Messengers

Second messengers are molecules that transmit signals received by cell surface receptors to the cell internal environment. In other words, they help deliver the information from the cell's exterior to its interior. There are different types of second messengers, but here we're only focusing on cAMP.

Hormone Background

Let's briefly describe each hormone: a. Testosterone - A male sex hormone (androgen) responsible for the development of secondary sexual characteristics and overall growth. b. Cortisol - A steroid hormone released by the adrenal cortex. It's responsible for regulating metabolism, immune response and stress response. c. Insulin - A hormone produced by the pancreas that helps regulate blood sugar (glucose) levels in the body. d. Epinephrine - Also known as adrenaline, it's a hormone and neurotransmitter responsible for the "fight or flight" response, which can increase heart rate, breathing rate, and blood flow to muscles.

Eliminating Hormones That Do Not Use cAMP

We can eliminate some of these hormones as not using cAMP as a second messenger, based on their mechanisms of action: a. Testosterone - As a steroid hormone, testosterone enters cells and acts directly on the DNA in the cell nucleus, so it does not rely on second messengers. b. Cortisol - Similar to testosterone, cortisol is a steroid hormone that directly enters cells, so it doesn't use cAMP as a second messenger. c. Insulin - Insulin is a peptide hormone that binds to the insulin receptor on the cell surface. This activates a signaling cascade involving the phosphorylation of several proteins, so it doesn't utilize cAMP as a second messenger.

Identifying the Hormone That Uses cAMP

After ruling out the other hormones based on their mechanisms of action, we are left with one hormone: d. Epinephrine - Epinephrine binds to adrenergic receptors (a type of cell surface receptor), leading to the activation of a G protein, which in turn activates adenylate cyclase. Adenylate cyclase is an enzyme that converts ATP into cAMP, which then acts as a second messenger to transmit the signal within the cell. Therefore, the correct answer is:

Answer

d. Epinephrine