Physiology
- Chapter 5-control of cells by chemical messengers
- Receptors for intercellular messengers are most commonly
A. peripheral membrane
B. integral membrane proteins.
C. specialized phospholipids within the
D. nucleic
2. Activation of a receptor by a chemical messenger
A. occurs when the messenger binds to the ligand-binding site of the receptor
B. is the first step leading to the ultimate response of a cell to the messenger.
C. requires a change in receptor conformation.
D. Both occurs when the messenger binds to the ligand-binding site of the receptor and is the first step leading to the ultimate response of a cell to the messenger are correct.
E. All of the choices are correct.
3. Which of the following are common means by which binding of an intercellular chemical messenger with a cell’s receptor brings about an intracellular response?
A. opening or closing of specific ionic channels in the plasma membrane
B. activation of an intracellular second- messenger system
C. promoting or inhibiting the transcription of genes that code for the synthesis of cellular proteins
D. Both opening or closing of specific ionic channels in the plasma membrane and activation of an intracellular second- messenger system are correct
E. All of the choices are correct
4. The process whereby repeated exposure to a hormone can cause a decrease in the number of receptors for that hormone is called
A. competiotion
B. inhibition.
C. down regulation
D. antagonism
E. saturation.
5. Cocaine lowers the levels of a chemical messenger in the brain called enkephalin. Researchers have found the number of enkephalin receptors to be higher in cocaine addicts than non addicted people. This is an example of
A. saturation
B. up regulation
C. antagonism
D. affinity.
E. down regulation
6. Methadone is a drug given to treat heroin addicts. It works by binding to the same receptors as heroin but with greater affinity, thereby preventing heroin from binding. This is an example of
A. competition
B. down regulation
C. signal transduction
D. agonistic behavior.
E. None of the choices are correct
7. Methadone is a drug given to treat heroin addicts. It works by binding to the same receptors as heroin but without producing the same effects. Methadone is
a. an antagonist
B. an agonist
c. a second messenger
d. an effector
e. a kinase
8. Oxytocin is a peptide hormone that causes the smooth muscle of the uterus to contract, but it has no effect on the smooth muscle cells of the small intestine. This difference in responsiveness exists because
A. oxytocin is inactivated prior to reaching the smooth muscle cells of the intestine
B. intestinal smooth muscle cells do not contain the proper second messenger system
C. uterine smooth muscle cells contain specific receptors for oxytocin.
D. oxytocin is able to cross the plasma membrane of uterine cells but not intestinal cells
E. oxytocin is not delivered by the circulatory system to intestinal cells
9. Epinephrine activates the cyclic AMP pathway in liver cells. Therefore, epinephrine
A. probably binds a specific transmembrane receptor in these cells
B. elicits its response in liver cells through second messengers.
C. probably binds a receptor in the nucleus of liver cells
D. Both probably binds a specific transmembrane receptor in these cells and elicits its response in liver cells through second messengers are correct.
E. Both elicits its response in liver cells through second messengers and probably binds a receptor in the nucleus of liver cells are correct
10. At very low concentrations, epinephrine causes an artery to vasodilate. At higher concentrations epinephrine causes the same artery to constrict. How can these different effects be explained?
A. There is one type of epinephrine receptor that uses two second messenger systems
B. There are two types of epinephrine receptors with different affinities for epinephrine that use two different second messenger systems.
C. There are two types of receptors for epinephrine that use the same second messenger system
D. At higher concentrations epinephrine can pass through the plasma membrane and directly stimulate contraction within the cell.
11. The significance of plasma- membrane receptors for chemical regulators such as hormones and neurotransmitters is that
A. they allow the regulators to affect cell functions while preventing them from entering into the cell’s cytoplasm
B. they permit nonpolar chemical messengers to affect cell functions
C. they allow for signal amplification or a multiplier effect of the message
D. Both they allow the regulators to affect cell functions while preventing them from entering into the cell’s cytoplasm and they permit nonpolar chemical messengers to affect cell functions are correct.
E. All of the choices are correct
12. Cells can control their responsiveness to external chemical regulators by
A. increasing the number of their transmembrane receptors by exocytosis
B. decreasing the number of their transmembrane receptors by endocytosis.
C. uncoupling their receptors from the second message generator.
D. Both increasing the number of their transmembrane receptors by exocytosis and decreasing the number of their transmembrane receptors by endocytosis are correct.
E. Both decreasing the number of their transmembrane receptors by endocytosis and uncoupling their receptors from the second message generator are correct.
13. A ligand that is an effective agonist for a chemical messenger
A. may have a higher affinity than the messenger for the messenger’s receptor
B. may achieve 50 percent saturation of the messenger’s receptor at a lower concentration than that required by the messenger.
C. does not couple to the binding site of the messenger’s receptor
D. Both may have a higher affinity than the messenger for the messenger’s receptor and may achieve 50 percent saturation of the messenger’s receptor at a lower concentration than that required by the messenger are correct
E. All of the choices are correct
14. Transcriptional regulation by a nonpolar hormone involves . The activation of an effector protein by protein kinase involves .
A. allosteric modulation/covalent modulation
B. kinase dephosphorylatlion/kinase phosphorylation
C. peptide hormones/steroid hormones
D. Both allosteric modulation/covalent modulation and kinase dephosphorylatlion/kinase phosphorylation are correct
E. Both allosteric modulation/covalent modulation and peptide hormones/steroid hormones are correct.
15. A fat cell responds to the presence of the hormone epinephrine by increasing cytosolic cyclic AMP production, which leads to the catabolism of both glycogen and fat. The best explanation for this phenomenon is:
A. Epinephrine is binding to two types of receptors in the plasma membrane
B. The activated receptor complex stimulates production of two different second messengers
C. Cyclic AMP can directly activate two kinds of enzymes.
D. Cyclic-AMP-dependent protein kinase can activate two kinds of enzymes.
E. All of the choices are
16. Which of the following questions about G proteins is not correct? G proteins may
A. act as second messenger
B. be stimulatory for second- messenger
C. be inhibitory for second- messenger production.
D. act as transducers for activated receptors by opening or closing ion channels
E. do none of the choices.
17. Activation of a receptor that is coupled by G proteins to adenylyl cyclase
A. may increase the intracellular concentration of cyclic AMP.
B. may decrease the intracellular concentration of cyclic AMP
C. may result in stimulation or inhibition of DNA transcription.
D. Both may increase the intracellular concentration of cyclic AMP and may decrease the intracellular concentration of cyclic AMP are correct.
E. All of the choices are correct.
18. Second messengers
A. are necessary for all receptor signal-transduction mechanism
B. act in the cell cytoplasm.
C. act as intracellular messengers
D. always function to activate enzymes
E. are always proteins.
19. Which of the following statements is true?
A. Phosphorylation by protein kinase can stimulate or inhibit the activity of effector proteins
B. Ca2+ and cyclic AMP are second messengers
C. Phosphodiesterase converts GMP into cGMP.
D. Both phosphorylation by protein kinase can stimulate or inhibit the activity of effector proteins and Ca2+ and cyclic AMP are second messengers are correct
E. All of the choices are
20. Which of the following are known to be second messengers?
A. diacylglycerol
B. phospholipase C
C. ATP
D. Both diacylglycerol and phospholipase C are correct.
E. All of the choices are
21. Amplification during a second messenger cascade is beneficial because amplification
a. takes small molecules and makes polymers out of them.
b. results in the production of more of the first messenger.
c. allows a cell to respond to more different hormones.
d. allows small amounts of hormones to produce large responses in target cells.
e. None of the choices are correct.
22. Amplification of a second messenger cascade can take place at this level:
a. 1 activated receptor can activate numerous G-proteins.
b. 1 activated G-protein can activate numerous effector enzymes.
c. 1 active effector enzyme can catalyze numerous reactions.
d. 1 activated protein kinase can allosterically modulate numerous proteins.
e. All of the choices are correct.
- Which of the following is not associated with the signal transduction of membrane-bound receptors?
a. phosphorylation (or autophosphorylation) of the intracellular portion of the receptor
b. calcium
c. transcription factors
d. calmodulin
e. None of the choices are correct.
24. calcium ion
a. concentration in the cytosol is increased by activation of phospholipase C.
b. concentration in the cytosol is increased by activation of membrane calcium channels.
c. release from the endoplasmic reticulum may be triggered by entry of calcium ion from the
extracellular fluid.
d. Both concentration in the cytosol is increased by activation of phospholipase C and concentration in the cytosol is increased by activation of membrane calcium channels are correct.
e. All of the choices are correct.
25. The second messenger that causes calcium ion to be released from intracellular stores is
a. diacylglycerol.
b. adenylyl cyclase.
c. inositol triphosphate.
d. phospholipase A.
e. None of the choices are correct.