Berg 8e testbank chapter 14 PDF

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Berg 8e testbank chapter 14...

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Chapter 14 Signal-Transduction Pathways Multiple-Choice Questions

1)

What is the primary messenger that is released by the adrenal gland?

A) B) C) D) E)

dopamine epinephrine glucagon insulin acetylcholine

Answer: B Section: Introduction and 14.1

2)

Which of the following is another name for a seven-transmembrane helix receptor?

A) B) C) D) E)

tyrosine kinase receptor ion channel receptor enzyme-linked receptor β-adrenergic receptor None of the answers is correct.

Answer: D Section: 14.1

3) What is covalently attached to the  and  subunits of heterotrimeric G proteins in order to anchor the protein to the cell membrane? A) B) C) D) E)

galactose N-acetylgalactosamine cholesterol phosphatidyl serine fatty acid

Answer: E

Section: 14.1

4)

What enzyme becomes active when bound to Ca2+ and diacylglycerol?

A) B) C) D) E)

calmodulin protein kinase A protein kinase C phospholipase C adenylate cyclase

Answer: C Section: 14.1

5)

Which of the following is the inactive form of protein kinase A?

A) R2C2 B) R4C2 C) R2C4 D) R4C4 E) None of the answers is correct. Section: 14.1

Answer: A

6)

What family of proteins contains the Ras proteins?

A) B) C) D) E)

GAP proteins G-protein receptor kinases small G proteins seven-transmembrane helix receptors heterotrimeric G proteins

Answer: C Section: 14.3

7) What is a gene that leads to the transformation of susceptible cell types into cell types with cancer-like characteristics? A) B) C) D) E)

protogene retrogene epigene oncogene None of the answers is correct.

Answer: D Section: 14.5

8) What eukaryotic protein serves as an intracellular Ca2+ sensor by binding to four calcium ions? A) B) C) D) E)

calmodulin phospholipase C protein kinase C vitamin D-dependent calcium binding protein calcitonin

Answer: A Section: 14.1

9)

What is a gene that contributes to cancer development only when deleted or damaged?

A) B) C) D) E)

oncogene proto-oncogene viral oncogene carcinoma-suppressor gene tumor-suppressor gene

Answer: E Section: 14.5

10)

What enzyme catalyzes the cleavage of PIP2?

A)

phospholipase A

B) C) D) E)

phospholipase C phospholipase D phospholipase P None of the answers is correct.

Answer: B Section: 14.1

Fill-in-the-Blank Questions 11. Protein kinase A phosphorylates serine and ___________ residues. Ans: threonine Section: 14.1 12. ____________ is the membrane protein that catalyzes the conversion of ATP to cAMP. Ans: Adenylate cyclase Section: 14.1 13. The cytosolic side, or β subunit, of the insulin receptor is a ________________ kinase. Ans: tyrosine Section: 14.2 14. The ________ receptor is approximately 50% identical in amino acid sequence with the EGF receptor and has similar domain structure, but it does not bind any known ligand. Ans: HER2 Section: 14.3 15. Important second messengers include cAMP, cGMP, calcium ion, _______________________, and diacylglycerol. Ans: inositol 1,4,5-trisphosphate (IP3) Section: Introduction 16. Input from several signaling pathways is called _____________________. Ans: cross talk Section: 14.1 and 14.4 17. _______________________ binds to the extracellular side of β-adrenergic receptors. Ans: Epinephrine Section: 14.1 18. The binding of IP3 to the IP3 receptor results in the release of __________ from the endoplasmic reticulum. Ans: calcium ions Section: 14.1 19. The catalytically active form of the insulin receptor is a result of phosphorylation of specific ____________ residues in the activation loop. Ans: tyrosine Section: 14.2

20. EGF signaling is terminated by the action of phosphatases and the hydrolysis of bound _____________ by Ras. Ans: GTP Section: 14.3

Multiple-Choice Questions 21) Most signal molecules A) easily diffuse through the membrane and bind to a receptor in the cytoplasm. B) bind to membrane receptors and transmit information across a membrane without traversing the membrane. C) carry out functions in the nucleus after binding to a receptor in the cell membrane. D) easily diffuse through the membrane and bind to a receptor in the nucleus. E) None of the answers is correct. Ans: B Section: Introduction 22) Examples of second messengers include A) B) C) D) E)

cAMP. calcium. inositol 1,4,5-trisphosphate. cGMP. All of the answers are correct.

Ans: E Section: Introduction 23) Advantages of second messengers include A) B) C) D) E)

the signal can be amplified by making many second messengers. second messengers can freely diffuse to other sites within the cell. a few common second messengers can be used in multiple signaling pathways. All of the answers are correct. A and C.

Ans: D Section: Introduction

24) Which of the following amino acids can be phosphorylated? A) B) C) D) E)

Tyr, Ser, Thr Tyr, Ser, Trp Ser, Thr, Asn His, Ser, Phe Tyr, Met, Trp

Ans: A Section: 14.1 25) Which form of the guanyl nucleotide is bound to a G protein in its unactivated state? A) GTP B) GDP C) GMP D) dGTP E) None of the answers is correct. Ans: B Section: 14.1 26) Which of the following is a common example of a mechanism by which a signaling process might be terminated? A) B) C) D) E)

change in temperature aggregation of all protein subunits protein dephosphorylation by phosphatases All of the answers are correct. None of the answers is correct.

Ans: C Section: 14.1 27) How does the binding of epinephrine to its receptor set a response in action? A) B) C) D)

It causes an exchange of GTP for G protein bound GDP. It causes a pore to open, allowing proton/ion exchange. It causes the release of insulin. It causes G proteins to produce cGMP.

E)

None of the answers is correct.

Ans: A Section: 14.1 28) Why is bound GTP considered a “clock”? A) B) C) D) E)

It is always produced and degraded in specific time intervals. It is regulated by energy. The G receptors have intrinsic GTPase activity, hydrolyzing GTP to GDP and Pi. It spontaneously hydrolyzes in the binding site of G proteins. None of the answers is correct.

Ans: C Section: 14.1 29) The enzyme responsible for induction of the phosphoinositide cascade is A) B) C) D) E)

phospholipase C. phospholipase A. C-dependent protein (CDP). calmodulin. None of the answers is correct.

Ans: A Section: 14.1 30) Common elements that occur in many signal transduction pathways include which of the following? A) B) C) D) E)

Specialized domains mediate specific interactions in the pathway. Second messengers may participate. Cell division is usually the result. A and B All of the answers are correct.

Ans: D Section: 14.4 31) How is calmodulin activated? A) by binding both calcium and potassium

B) C) D) E)

by binding Ca2+ when the cytosolic concentration is greater than 500 nM by binding to a positively charged helix on another protein by binding Ca2+ only when calcium channels are open, allowing Ca2+ efflux from the cell None of the answers is correct.

Ans: B Section: 14.1 32) Cross-phosphorylation of the EGF receptor is possible when two receptor proteins A) B) C) D) E)

are cleaved. dimerize. are internalized into organelles. covalently cross link. None of the answers is correct.

Ans: B Section: 14.2 and 14.3 33) Which of the following is an example of a disease that is caused by altered G-protein activity? A) B) C) D) E)

whooping cough cholera bubonic plague whooping cough and cholera whooping cough and bubonic plague

Ans: D Section: 14.5 34) ______________ may be effective anti-cancer drugs. A) Monoclonal antibodies against offending receptors B) EGF mimics C) Protein kinase inhibitors D) All of the answers are correct. E) Both monoclonal antibodies against offending receptors and protein kinase inhibitors Ans: C Section: 14.5

35) The v and c in v-src and c-src refer to A) B) C) D) E)

viral and cellular. viral and cytosolic. viral and cystic. Vibrio and cholera. None of the answers is correct.

Ans: A Section: 14.5

Short-Answer Questions 36) What are some of the common structural features of the receptors to which signal molecules bind? Ans: The molecule must have a signal-binding site on the extracellular side of the membrane and must have an intracellular domain. Binding of the ligand to the receptor must induce change into another form that affects the shape of the intracellular portion, so the signal can be transmitted. Section: Introduction 37) What is a disadvantage of using common molecules for signaling paths? Ans: When second messengers are involved in more than one signaling pathway, fine tuning and sensitive responses can result. However, when the cross-talk becomes inappropriate, the signaling paths and responses will be in error. Section: Introduction 38) What happens when signaling paths are not terminated properly? Ans: The cell will not be able to respond properly to new stimuli. The errant signals may lead to cancer, especially if there is uncontrolled cell growth. Section: Introduction 39) How many 7TM membranes exist? What are some of their functions? Ans: There are estimated to be thousands of 7TM receptors. Functions they mediate include sensory signaling, physiological control, exocytosis, chemotaxis, neurotransmission, cell development and growth, and viral infection. (See Table 14.1 of the textbook for a more complete list.) Section: 14.1 40) What is the general mechanism for signal transmission by 7TM receptors?

Ans: The receptors “snake” through a membrane, with domains extending on the extracellular and cytoplasmic sides. A ligand binds to a site on the extracellular side, inducing a conformation change that is detectable on the cytoplasmic side of the cell. Section: 14.1 41) How does binding of epinephrine initiate cAMP production? Discuss briefly in terms of receptor structure and function. Ans: Epinephrine binds to a 7TM receptor which interacts with heterotrimeric G protein, causing it to exchange GDP with GTP. The binding of GTP causes the G protein to dissociate and the active Gα – GTP complex binds to the enzyme, adenylate cyclase. Adenylate cyclase is a large membrane-embedded protein, with two large domains located on the inside of the cell. This interaction induces a conformational change in the enzyme resulting in a more catalytically active form, thus more cAMP is made. (See Figure 14.8 of the textbook for more detail.) Section: 14.1 42) How is the hormone-bound activated receptor reset after activation? Ans: The hormone dissociates, and the receptor returns to its initial state. In addition, phosphorylation of specific residues leads to the binding of β–arrestin, which further diminishes its ability to activate G proteins. Section: 14.1 43) What are receptor tyrosine kinases? Provide an example. Ans: These are proteins that bind ligands, such as EGF or insulin, on the extracellular domain. They also contain tyrosine kinase domains on the intracellular side. Section: 14.1 and 14.2 44) What is the difference between an oncogene and a proto-oncogene? Ans: An oncogene, such as v-src, leads to the generation of cancer-like characteristics in susceptible cell types. A proto-oncogene, such as c-src, does not induce cell transformation but refers to the fact that this gene, when mutated, can be converted into an oncogene. Section: 14.5 45) In addition to its range in concentration, what other property of calcium ion makes it a highly suitable messenger? Ans: It can bind tightly to proteins because it forms between six and eight interactions with protein ligands or water. These extensive interactions allow calcium ions to mediate large conformational changes in proteins. Section: 14.1 46) What is meant by an EF hand? Draw or describe the structure.

Ans: The EF hand is a protein that binds calcium ions and contains a calcium ion-binding domain that contains a helix-loop-helix arrangement. The structure resembles a hand, index finger and thumb extended, with the ion held near the palm by the middle finger. Figure 14.17 of the textbook is an example of what a drawing of this structure may look like. Section: 14.2 47) Draw the reaction catalyzed by tyrosine kinase (no mechanism necessary). Ans: O

OH ATP

H

N

ADP

Tyrosine kinase

H C O

PO 3-2

H H

N

C O

Section: 14.2 48) What is the relationship between monoclonal antibodies, breast cancer, and HER2? Ans: HER2 is a membrane protein that is very similar to the EGF receptor protein except it does not bind any known ligand. It can participate in cross-phosphorylation reactions with other receptors activating signaling pathways such as the EGF pathway. HER2 is overexpressed in about 30% of breast cancers. Monoclonal antibodies to HER2 have been used to treat cancers in these patients. Section: 14.3, 14.5 49) What is the difference between heterotrimeric G proteins and small G proteins? Ans: Heterotrimeric G proteins are composed of αβγ subunits. The α subunit contains the guanyl nucleotide binding site. Upon activation by the signal-receptor event, the GDP is exchanged with a GTP, and the βγ subunits dissociate from the α bound with GTP. The resulting Gα is the form that activates adenyl cyclase. Small G proteins, such as Ras, are single subunit proteins. They are activated by proteins such as Sos in the EGF signal pathway, which allows GTP to replace GDP, converting Ras into its activated form. Section: 14.1 and 14.3 50) Describe two roles of phosphatidylinositol 4,5-bisphosphate (PIP2) in signal transduction. Ans: 1. PIP2 is one of the signal molecules in the insulin pathway. It is converted into PIP3 by phosphoinositide 3-kinase. The binding of PIP3 activates PIP3-dependent protein kinase, which phosphorylates and activates other kinases in the insulin pathway. 2. PIP2 is also involved in another signal pathway that is activated by angiotensin II. The angiotensin II receptor activates phospholipase C, which hydrolyses PIP2 to produce diacylglycerol (DAG) and inositol 1,4,5-

trisphosphate (IP3). The DAG binds to and activates protein kinase C (PKC), and the IP3 binds to an IP3 receptor in the endoplasmic reticulum that is also a calcium ion channel. This opens the channel and calcium ions are released into the cytoplasm. The calcium ions bind to PKC and facilitate its activation. Section 14.1...