16. The Endocrine System

What is the role of G proteins in GPCR signaling?

Hormones can bring about substantial physiological changes at very low concentrations. How does this relate to the concept of second messenger systems?

You are studying how a hormone affects a cell and find that when oxytocin binds the receptor, the intracellular $Ca$$^2$$^+$ concentration increases. Based on this information, what could you logically conclude about this cell and hormone?

cAMP, $IP_3$, and DAG are all molecules that are used as secondary messengers. Which statement below correctly identifies a difference between the pathways in which they are found?

Some hormones act by:

a. Increasing the synthesis of enzymes

b. Converting an inactive enzyme into an active enzyme

c. Affecting only specific target organs

d. All of these

Cyclic AMP functions as a second messenger to:

(a) Build proteins and catalyze specific reactions

(b) Activate adenylate cyclase

(c) Open ion channels and activate key enzymes in the cytoplasm

(d) Bind the hormone–receptor complex to DNA segments

How would blocking the activity of phosphodiesterase (PDE) affect a cell that responds to hormonal stimulation by the cAMP second messenger system?

A researcher observes that stimulation by a particular hormone induces a marked increase in the activity of G proteins in the target plasma membrane. The hormone being studied is probably:

(a) A steroid

(b) A peptide

(c) Testosterone

(d) Estrogen

(e) Aldosterone