1. The stimulus for secretion of neurotransmitters into the synaptic cleft is an increase in
A) sodium levels.
B) calcium levels.
C) neurotransmitter levels.
D) chloride levels.
E) potassium levels.

2. Multiple sclerosis is a result of
A) the absence of myelin on nerve cells.
B) having excess acetylcholine receptors.
C) blocking the nodes on Ranvier.
D) excess amounts of myelin on nerve cells.
E) an immune system attack on nerve fibers.

3. Name for the phase at the end of an action potential when the membrane potential becomes more negative than it is at rest is the ________ phase.
A) threshold
B) refractory
C) hyperpolarizing
D) depolarizing
E) repolarizing

4. To have a hormone receptor system that is responsive to changes in hormone concentration, it is useful if the concentration of the hormone is
A) far below the Kd before the stimulation of hormone secretion.
B) always more than 10 times the Kd.
C) always constant.
D) never more than 10 times the Kd.
E) far above the Kd before the stimulation of hormone secretion.

5. Desensitization of a cell to a ligand may involve all BUT
A) receptor-mediated endocytosis.
B) destruction of the ligand.
C) lowered affinity of a receptor for the ligand.
D) a lessened response to the ligand.
E) receptor down-regulation.

6. Base your answers to the problems below on the following information:
You have isolated a factor from the blood of a space alien and named it XFF (for X-files factor). Based on preliminary data, you think that XFF could be one of three compounds normally found in human blood: epidermal growth factor (EGF), epinephrine, or estrogen.

You obtain two different preparations of XFF, one of which contains the receptors for XFF. You perform a binding assay and obtain a standard curve. Based upon this data, what value would reflect the affinity of the receptor for the ligand? (Assume a 1 XFF to 1 receptor interaction.)
A) Kd - Bmax
B) Bmax
C) Kd
D) 1/Bmax
E) This information cannot be obtained in this manner.

7. G protein-adenyl cyclase activity has been shown, in some cases, to be associated with certain diseases. In the case of cholera, which of the following is NOT correct?
A) Vibrio cholera bacteria colonize the gut.
B) Cholera toxin is secreted by Vibrio cholera bacteria.
C) Cholera toxin alters Gs so that it no longer hydrolyzes GTP.
D) The toxin, by altering Gs, keeps intracellular cAMP levels high and doesn't allow them to decrease.
E) The cholera toxin causes the cells of the gut to take in salts and fluids.

8. With regard to hormones, responses occurring over the shortest distance would be classified as
A) exocrine.
B) endocrine.
C) paracrine.
D) Choices A, B, and C all act over the same distance.
E) none of the above

9. Kinases and phosphatases are essential in the cell because they
A) are enzymes that destroy damaged proteins.
B) help turn proteins "on and off" through changes in phosphorylation status.
C) sense short poly A tails in mRNA as a signal to degrade the mRNA.
D) destroy second messengers, thereby turning off a signal transduction pathway.
E) all of the above

10. Kinases are enzymes that
A) add phosphate groups.
B) remove phosphate groups.
C) do not alter target activity.
D) are always inhibitory.
E) all of the above.

11. Phosphatases are enzymes that
A) do not alter target activity.
B) remove phosphate groups.
C) add phosphate groups.
D) are always inhibitory.
E) all of the above

12. All of the following are second messengers, EXCEPT
A) inositol trisphosphate.
B) cyclic adenosine monophosphate.
C) diacylglycerol.
D) epinephrine.
E) calcium ions.