Cell and Molecular Biology: Concepts and Experiments

Gerald Karp

Chapter 15

Cell Signaling and Signal Transduction: Communication Between Cells - all with Video Answers

Educators

Chapter Questions

Problem 1

The subject of cell signaling was placed near the end of the book because it ties together so many different topics in cell biology. Now that you have read the chapter, would you agree or disagree with this statement? Support your conclusions by example.

Bryan Valdivia

Bryan Valdivia

Numerade Educator

Problem 2

Suppose the signaling pathway in Figure 15.3 were to lead to the activation of a gene that inhibits a cyclin-dependent kinase responsible for moving a cell into S phase of the cell cycle. How would a debilitating mutation in protein kinase 3 affect the cell's growth?

Bryan Valdivia

Numerade Educator

Problem 3

What might be the effect on liver function of a mutation in a gene that encodes a cAMP phosphodiesterase? of a mutation in a gene encoding a glucagon receptor? of a mutation in a gene encoding phosphorylase kinase? of a mutation that altered the active site of the GTPase of a G. subunit? (Assume in all cases that the mutation causes a loss of function of the gene product.)

Bryan Valdivia

Numerade Educator

Problem 4

$\mathrm{Ca}^{2+}, \mathrm{IP}_{3},$ and $\mathrm{cAMP}$ have all been described as second messengers. In what ways are their mechanisms of action similar? In what ways are they different?

Emily Himsel

Numerade Educator

Problem 5

In the reaction cascade illustrated in Figure $15.22,$ which steps lead to amplification and which do not?

Sana Riaz

Numerade Educator

Problem 6

Suppose that epinephrine and norepinephrine could initiate a similar response in a particular target cell. How could you determine whether or not the two compounds act by binding to the same cell-surface receptor?

Sana Riaz

Numerade Educator

Problem 7

One of the key experiments to show that gap junctions (page 262 ) allowed the passage of small molecules was carried out by allowing cardiac muscle cells (which respond to norepinephrine by contraction) to form gap junctions with ovarian granulosa cells (which respond to FSH by undergoing various metabolic changes). The researchers then added FSH to the mixed cell culture and observed the contraction of the muscle cells. How could muscle cells respond to $\mathrm{FSH}$, and what does this tell you about the structure and function of gap junctions?

Sana Riaz

Numerade Educator

Problem 8

How would you expect a GTP analogue that the cell could not hydrolyze (a nonhydrolyzable analogue) to affect signaling events that take place during the stimulation of a liver cell by glucagon? What would be the effect of the same analogue on signal transduction of an epithelial cell after exposure to epidermal growth factor (EGF)? How would this compare to the effects of the cholera toxin (page 627 ) on these same cells?

Bryan Valdivia

Numerade Educator

Problem 9

You suspect that phosphatidylcholine might be serving as a precursor for a second messenger that triggers secretion of a hormone in a type of cultured endocrine cell that you are studying. Furthermore, you suspect that the second messenger released by the plasma membrane in response to a stimulus is choline phosphate. What type of experiment might you perform to verify your hypothesis?

Sana Riaz

Numerade Educator

Problem 10

Figure 15.27 shows the localized changes in $\left[\mathrm{Ca}^{2+}\right]$ within the dendritic tree of a Purkinje cell. Calcium ions are small, rapidly diffusible agents. How is it possible for a cell to maintain different concentrations of this free ion in different regions of its cytosol? What do you suspect would happen if you injected a small volume of a calcium chloride solution into one region of a cell that had been injected previously with a fluorescent calcium probe?

Sana Riaz

Numerade Educator

Problem 11

Formulate a hypothesis that might explain how contact of the outer surface of an egg by a fertilizing sperm at one site causes a wave of $\mathrm{Ca}^{2+}$ release that spreads through the entire $\mathrm{egg}$, as shown in Figure 15.29

Sana Riaz

Numerade Educator

Problem 12

Because calmodulin activates many different effectors (e.g., protein kinases, phosphodiesterases, calcium transport proteins), a calmodulin molecule must have many different binding sites on its surface. Would you agree with this statement? Why or why not?

Sana Riaz

Numerade Educator

Problem 13

Diabetes mellitus is a disease that can result from a number of different defects involving insulin function. Describe three different molecular abnormalities in a liver cell that could cause different patients to exhibit a similar clinical picture, including, for ecample, high concentrations of glucose in the blood and urine.

Bryan Valdivia

Numerade Educator

Problem 14

Would you expect a cell's response to EGF to be more sensitive to the fluidity of the plasma membrane than its response to insulin? Why or why not?

Emily Himsel

Numerade Educator

Problem 15

Would you expect a mutation in Ras to act dominantly or recessively as a cause of cancer? Why? (A dominant mutation causes its effect when only one of the homologous alleles is mutated, whereas a recessive mutation requires that both alleles of the gene are mutated.)

Bryan Valdivia

Numerade Educator

Problem 16

Speculate on a mechanism by which apoptosis might play a crucial role in combating the development of cancer, a topic discussed in the following chapter.

Bryan Valdivia

Numerade Educator

Problem 17

You are working with a type of fibroblast that normally responds to epidermal growth factor by increasing its rate of growth and division, and to epinephrine by lowering its rate of growth and division. You have determined that both of these responses require the MAP kinase pathway, and that EGF acts by means of an RTK and epinephrine by means of a G protein-coupled receptor. Suppose you identified a mutant strain of these cells that can still respond to EGF but is no longer inhibited by epinephrine. You suspect that the mutation is affecting the cross-talk between two pathways (shown in Figure 15.35 ). Which component in this figure might be affected by such a mutation?

Sana Riaz

Numerade Educator

Problem 18

In what way is the calcium wave that occurs at fertilization $\operatorname{sim}^{-}$ ilar to a nerve impulse that travels down a neuron?

Emily Himsel

Numerade Educator

Problem 19

Now that you have read the section on taste perception, why do you suppose it has been difficult to find effective rat poisons?

Emily Himsel

Numerade Educator

Problem 20

One of the genes of the cowpox virus encodes a protein called CrmA that is a potent inhibitor of caspases. What effect would you expect this inhibitor to have on an infected cell? Why is this advantageous to the infecting virus?

Bryan Valdivia

Numerade Educator

Problem 21

Most RTKs act directly on downstream effectors, whereas the insulin RTK acts through an intermediate docking protein, an insulin receptor substrate (IRS). Are there any advantages in signaling that might accrue from the use of these IRS intermediates?

Sana Riaz

Numerade Educator

Problem 22

Researchers have reported that (1) most of the physiologic effects of insulin on target cells can be blocked by incubation of cells with workingwoman, a compound that specifically inhibits the enzyme PI3K and (2) that causing cells to over-express a constructively active form of PKB (i.e., a form of the enzyme that is continually active regardless of circumstances) induces a response in cells that is virtually identical to addition of insulin to these cells. Looking at Figure $15.25,$ are these observations ones that you might have predicted? Why or why not?

Sana Riaz

Numerade Educator

Problem 23

Knockout mice that are unable to produce caspase- 9 die as a result of a number of defects, most notably a greatly enlarged brain. Why would these mice have this phenotype? How would you expect the phenotype of a cytochrome $\epsilon$ knockout mice to compare with that of the caspase- 9 knockout?

Bryan Valdivia

Numerade Educator

Problem 24

Why do you suppose that some people find a compound called PROP to have a bitter taste, whereas others do not report this perception?

Bryan Valdivia

Numerade Educator

Problem 25

The inhibition of a specific protein kinase often leads to an increased phosphorylation of many cellular proteins. How can you explain this observation?

Bryan Valdivia

Numerade Educator