Question 1

You are interested in cell-size regulation and discover that signaling through an enzyme-coupled receptor is important for the growth (enlargement) of mouse liver cells.Activation of the receptor activates adenylyl cyclase, which ultimately leads to the activation of PKA, which then phosphorylates a transcription factor called TFS on threonine 42.This phosphorylation is necessary for the binding of TFS to its specific sites on DNA, where it then activates the transcription of Sze2, a gene that encodes a protein important for liver cell growth.You find that liver cells lacking the receptor are 15% smaller than normal cells, whereas cells that express a constitutively activated version of PKA are 15% larger than normal liver cells.Given these results, predict whether you would expect the cell's size to be bigger or smaller than normal cells if cells were treated in the following fashion.
A.You change threonine 42 on TFS to an alanine residue.
B.You create a version of the receptor that is constitutively active.
C.You add a drug that inhibits adenylyl cyclase.
D.You add a drug that increases the activity of cyclic AMP phosphodiesterase.
E.You mutate the cAMP-binding sites in the regulatory subunits of PKA, so that the complex binds cAMP more tightly.

Accepted Answer

The answer of You are interested in cell-size regulation and...

Question 2

The following happens when a G-protein-coupled receptor activates a G protein.

Accepted Answer

A) The β subunit exchanges its bound GDP for GTP. 
B) The GDP bound to the α subunit is phosphorylated to form bound GTP. 
C) The α subunit exchanges its bound GDP for GTP. 
D) It activates the α subunit and inactivates the βγ complex.

Question 3

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

Accepted Answer

The answer of Explain why the signal molecules used in...

Question 4

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells.Delta is involved in __________ signaling.

Accepted Answer

A) endocrine 
B) paracrine 
C) neuronal 
D) contact-dependent

Question 5

List in order the following types of cell signaling from the type of signaling in which the signal molecule travels the least distance to the type of signaling in which the signal molecule travels the largest distance.
contact-dependent signaling neuronal signaling
endocrine signaling paracrine signaling

Accepted Answer

The answer of List in order the following types of...

Question 6

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to

Accepted Answer

A) activate the RTK. 
B) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane. 
C) directly phosphorylate Akt. 
D) create DAG.

Question 7

Figure 16-36 shows how normal signaling works with a Ras protein acting downstream of an RTK.You examine a cell line with a constitutively active Ras protein that is always signaling.Which of the following conditions will turn off signaling in this cell line?  Figure 16-36

Accepted Answer

A) addition of a drug that prevents protein X from activating Ras 
B) addition of a drug that increases the affinity of protein Y and Ras 
C) addition of a drug that blocks protein Y from interacting with its target 
D) addition of a drug that increases the activity of protein Y

Question 8

Which of the following mechanisms is NOT directly involved in inactivating an activated RTK?

Accepted Answer

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

Question 9

Antibodies are Y-shaped molecules that have two identical binding sites.Suppose that you have obtained an antibody that is specific for the extracellular domain of an RTK.When the antibody binds to the RTK, it brings together two RTK molecules.If cells containing the RTK were exposed to the antibody, would you expect the kinase to be activated, inactivated, or unaffected? Explain your reasoning.

Accepted Answer

The answer of Antibodies are Y-shaped molecules that have two...

Question 10

Cell lines A and B both survive in tissue culture containing serum but do not proliferate.Factor F is known to stimulate proliferation in cell line A.Cell line A produces a receptor protein (R) that cell line B does not produce.To test the role of receptor R, you introduce this receptor protein into cell line B, using recombinant DNA techniques.You then test all of your various cell lines in the presence of serum for their response to factor F, with the results summarized in Table 16-9. $\begin{array} { l l l } 
\text { Cell line } & \text { Factor } F & \text { Response } \
\hline \text { A } & \text { - Factor F } & \text { Cells do not proliferate } \
\text { A } & \text { + Factor F } & \text { Cells proliferate } \
\text { B } & \text { - Factor F } & \text { Cells do not proliferate } \
\text { B } & \text { + Factor F } & \text { Cells do not proliferate } \
\text { B + receptor R } & \text { - Factor } F & \text { Cells proliferate } \
\text { B + receptor R } & \text { + Factor F } & \text { Cells proliferate }
\end{array}$ Table 16-9
Which of the following cannot be concluded from your results above?

Accepted Answer

A) Binding of factor F to its receptor is required for proliferation of cell line A. 
B) Receptor R binds to factor F to induce cell proliferation in cell line A. 
C) Cell line A expresses a receptor for factor F. 
D) Factor F is not required for proliferation in cell line B.

Question 11

Choose the phrase in each pair that is likely to occur more rapidly in response to an extracellular signal.
A.changes in cell secretion/increased cell division
B.changes in protein phosphorylation/changes in proteins being synthesized
C.changes in mRNA levels/changes in membrane potential

Accepted Answer

The answer of Choose the phrase in each pair that...

Question 12

When Ras is activated, cells will divide.A dominant-negative form of Ras clings too tightly to GDP.You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras.Which of the following statements is TRUE?

Accepted Answer

A) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras. 
B) The cells you create will run out of the GTP necessary to activate Ras. 
C) The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras. 
D) The normal Ras in the cells you create will not be able to bind GDP because the dominant-negative Ras binds to GDP too tightly.

Question 13

Indicate by writing "yes" or "no" whether amplification of a signal could occur at the particular steps described below.Explain your answers.
A.An extracellular signaling molecule binds and activates a GPCR.
B.The activated GPCRs cause Gα to separate from Gβ and Gγ.
C.Adenylyl cyclase produces cyclic AMP.
D.cAMP activates protein kinase A.
E.Protein kinase A phosphorylates target proteins.

Accepted Answer

The answer of Indicate by writing "yes" or "no" whether...

Question 14

The growth factor Superchick stimulates the proliferation of cultured chicken cells.The receptor that binds Superchick is a receptor tyrosine kinase (RTK), and many chicken tumor cell lines have mutations in the gene that encodes this receptor.Which of the following types of mutation would be expected to promote uncontrolled cell proliferation?

Accepted Answer

A) a mutation that prevents dimerization of the receptor 
B) a mutation that destroys the kinase activity of the receptor 
C) a mutation that inactivates the protein tyrosine phosphatase that normally removes the phosphates from tyrosines on the activated receptor 
D) a mutation that prevents the binding of the normal extracellular signal to the receptor

Question 15

The ethylene response in plants involves a dimeric transmembrane receptor.When the receptor is not bound to ethylene, the receptor binds to and activates a protein kinase, which activates an intracellular signaling pathway that leads to the degradation of a transcriptional regulator important for transcribing the ethylene-responsive genes (see Figure 16-33).You discover a phosphatase that is important for ethylene signaling, and you name it PtpE.Plants lacking PtpE never turn on ethylene-responsive genes, even in the presence of ethylene.You find that PtpE dephosphorylates serine 121 on the transcriptional regulator.Furthermore, plants lacking PtpE degrade the transcriptional regulator in the presence of ethylene. (A) $\text { ABSENCE OF ETHYLENE }$

(B) $\text { PPESENCE OF ETHYLENE }$

Figure 16-33
Which of the following statements is inconsistent with your data?

Accepted Answer

A) When the transcriptional regulator is phosphorylated, it activates transcription of the ethylene-responsive genes. 
B) When the transcriptional regulator is not phosphorylated, it binds to DNA. 
C) Activation of the protein kinase that binds to the ethylene receptor leads to inactivation of PtpE. 
D) Binding of ethylene to its receptor leads to the activation of PtpE.

Question 16

Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2, as diagrammed in Figure 16-28.  Figure 16-28
Which of the following statements is FALSE?

Accepted Answer

A) In the presence of a survival signal, Akt is phosphorylated. 
B) In the absence of a survival signal, Bad inhibits the cell-death inhibitor protein Bcl2. 
C) In the presence of a survival signal, the cell-death inhibitory protein Bcl2 is active. 
D) In the absence of a survival signal, Bad is phosphorylated.

Question 17

When the neurotransmitter acetylcholine is applied to skeletal muscle cells, it binds the acetylcholine receptor and causes the muscle cells to contract.Succinylcholine, which is a chemical analog of acetylcholine, binds to the acetylcholine receptor on skeletal muscle cells but causes the muscle cells to relax; it is therefore often used by surgeons as a muscle relaxant.Propose a model for why succinylcholine causes muscle relaxation.What might be the mechanism to explain the different activities of acetylcholine and succinylcholine on the acetylcholine receptor?

Accepted Answer

The answer of When the neurotransmitter acetylcholine is applied to...

Question 18

When activated by the extracellular signal protein platelet-derived growth factor (PDGF), the PDGF receptor phosphorylates itself on multiple tyrosines (as indicated in Figure 16-61A by the circled Ps; the numbers next to these Ps indicate the amino acid number of the tyrosine).These phosphorylated tyrosines serve as docking sites for proteins that interact with the activated PDGF receptor.These proteins are indicated in the figure, and include the proteins A, B, C, and D.One of the cell's responses to PDGF is an increase in DNA synthesis, which can be measured by the incorporation of radioactive thymidine into the DNA.
To determine which protein or proteins-A, B, C, or D-are responsible for the activation of DNA synthesis, you construct mutant versions of the PDGF receptor that retain one or more tyrosine phosphorylation sites.You express these mutant versions in cells that do not make their own PDGF receptor.In these cells, the various mutant versions of the PDGF receptor are expressed normally, and, in response to PDGF binding, become phosphorylated on whichever tyrosines remain.You measure the level of DNA synthesis in cells that express the various mutant receptors and obtain the data shown in Figure 16-22B. (A)

(B)

Figure 16-22
A.From these data, which, if any, of proteins A, B, C, and D are involved in the stimulation of DNA synthesis by PDGF? Explain your answer.
B.Which, if any, of these proteins inhibit DNA synthesis? Explain your answer.
C.Which, if any, of these proteins seem to have no detectable role in DNA synthesis? Explain your answer.

Accepted Answer

The answer of When activated by the extracellular signal protein...

Question 19

Which of the following statements about G-protein-coupled receptors (GPCRs) is FALSE?

Accepted Answer

A) GPCRs are the largest family of cell-surface receptors in humans. 
B) GPCRs are used in endocrine, paracrine, and neuronal signaling. 
C) GPCRs are found in yeast, mice, and humans. 
D) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

Question 20

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by

Accepted Answer

A) activating a G protein. 
B) activating a receptor tyrosine kinase. 
C) diffusing into cells and stimulating the cyclase directly. 
D) activating an intracellular protein kinase.

Exam 16: Cell Signaling