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

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