1

Chapter 16 Cell Communication Questions For questions 1-5 chose answers from the list below. 1. A signal that must be relayed to the entire body is most efficiently sent by __________________ cells,

which produce hormones that are carried throughout the body through the bloodstream. 2. __________________ methods of cell signaling do not require the release of a secreted molecule and

are used for very localized signaling events.

3. During __________________ signaling, the signal remains in the neighborhood of the secreting cell and thus acts as a local mediator on nearby cells.

4. __________________ signaling converts electrical impulses into a chemical signal.

5. Cells receive signals through a __________________, which can be an integral membrane protein or can reside inside the cell.

A) amplification B) contact-dependent C) endocrine D) epithelial E) G-protein A+B) K+ channel A+C) neuronal A+D) paracrine A+E) phosphorylation B+C) receptor B+D) target

6. Rank the following types of cell signaling from 1 to 4, with 1 representing the type of signaling in which

the signal molecule travels the least distance and 4 the type of signaling in which the signal molecule travels the largest distance. ______ paracrine signaling ______ contact-dependent signaling ______ neuronal signaling ______ endocrine signaling

2

7. Explain why the signal molecules used in neuronal signaling work at a longer range than those used in contact-dependent signaling.

8. Which is likely to occur more rapidly in response to an extracellular signal.

A) changes in cell secretion B) increased cell division

9. Which is likely to occur more rapidly in response to an extracellular signal. A) changes in protein phosphorylation B) changes in proteins being synthesized 10. Which is likely to occur more rapidly in response to an extracellular signal. A) changes in mRNA levels B) changes in membrane potential 11. Receipt of extracellular signals can change cell behavior quickly (e.g., in seconds or less) or much

more slowly (e.g., in hours). A. What kind of molecular changes could cause quick changes in cell behavior? B. What kind of molecular changes could cause slow changes in cell behavior? C. Explain why the response you named in A results in a quick change, whereas the response you

named in B results in a slow change. 12. The figure below shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation

in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine?

A) a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO B) a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to

cyclic GMP

arginine

activatednerve terminal

endothelial cell smooth muscle cell

RAPID RELAXATIONOF SMOOTH MUSCLE CELLNO

RAPID DIFFUSION OF NOACROSS MEMBRANES

NO bound toguanylyl cyclase

cyclicGMP

acetylcholine

GTP

3

C) a muscle cell that has cyclic GMP phosphodiesterase constitutively active D) a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO E) the absence of extracellular calcium available to the nerve cell

For questions 13-18 chose answers from the list below. 13. G-protein-coupled receptors (GPCRs) all have a similar structure with

__________________ transmembrane domains.

14. When a GPCR binds an extracellular signal, an intracellular G protein, composed of __________________ subunits, becomes activated.

15. __________________ of the G-protein subunits are tethered to the plasma membrane by short lipid tails.

16. When unstimulated, the α subunit is bound to GDP, which is exchanged for __________________ on stimulation.

17. The intrinsic __________________ activity of the α subunit is important for inactivating the G protein.

18. __________________ inhibits this activity of the α subunit, thereby keeping the subunit in an active state.

A) phosphodiesterase B) GTP C) adenylyl cyclase D) seven E) two A+B) GDP A+C) diacylglycerol A+D) five A+E) GTPase B+C) cholera toxin B+D) AMP B+E) three C+D) ATPase C+E) Ca2+ D+E) cAMP

4

19. A protein kinase can act as an integrating device in signaling if it ___________________.

A) phosphorylates more than one substrate B) catalyzes its own phosphorylation C) is activated by two or more proteins in different signaling pathways D) initiates a phosphorylation cascade involving two or more protein kinases E) also has phosphatase activity

20. Which of the following mechanisms is not directly involved in inactivating an activated RTK? A) dephosphorylation by serine/threonine phosphatases B) dephosphorylation by protein tyrosine phosphatases C) removal of the RTK from the plasma membrane by endocytosis D) digestion of the RTK in lysosomes E) blocking the catalytic site in the RTK

5

Chapter 16 Cell Communication (Answers) 1. endocrine 2. contact-dependent

3. paracrine

4. euronal

5. receptor

6. paracrine signaling = 3 contact-dependent signaling = 1 neuronal signaling = 2 endocrine signaling = 4

7. The neurotransmitter released from a neuron in neuronal signaling must diffuse across the synaptic cleft to reach receptors on the target cell. In contrast, in contact-dependent signaling, the signal molecule is attached to the plasma membrane of the signaling cell and interacts with receptors located on the plasma membrane of the receiving cell; thus, the cells must be in direct contact for this type of signaling to occur.

8. A. 9. A. 10. B. 11. A. Any answer that involves the modification of existing cell components is correct. Protein

phosphorylation, protein dephosphorylation, protein ubiquitylation, lipid phosphorylation, and lipid cleavage are all examples of correct answers.

B. Responses that involve alterations in gene expression occur slowly. C. Modification of existing cellular components can happen quickly, whereas responses that

depend on changes in gene expression take much longer, because the genes will need to be transcribed, the mRNAs will need to be translated, and the proteins need to accumulate to high enough levels to instigate change.

6

12. B). A constitutively active guanylyl cyclase will produce cGMP even in the absence of a signal and thus

will lead to relaxation of smooth muscle cells in the absence of acetylcholine. Choice A) would lead to a block in the production of cGMP such that even if NO were to reach the smooth muscle cells, relaxation would not occur. Choice C) would not lead to muscle cell relaxation independently of acetylcholine, because cyclic GMP phosphodiesterase is involved in the degradation of cGMP. Choice D) will lead to a block in the production of NO. Choice E) would block the ability of neurotransmitter vesicles to fuse with the synaptic membrane.

13. seven 14. three. 15. two 16. GTP 17. GTPase 18. cholera toxin 19. C). Integrating devices are able to relay signals from more than one signaling pathway. Being activated

by two or more proteins in different signalling pathways different allows a kinase (or any other signaling molecule) to be affected by more than one upstream signal. Choices A), B), and D) affect the output signal that a kinase is able to produce, not its ability to integrate upstream signals from more than one signaling pathway. E) having phosphatase activity is not related to integration.

20. A). RTKs are phosphorylated on tyrosines by their dimerization partner, which is also a tyrosine kinase,

and thus the reversal of these phosphorylations involves protein tyrosine phosphotases, and not protein serine/threonine phosphatases. Endocytosis of the receptor and its ultimate digestion in the lysosome are other methods that the cell uses to downregulate active receptors.