Chapter 11 Biology 111

What is the precursor to cAMP in the given examples of cell signaling?

A) ATP

37) What explains the increased concentration of Ca++ in the ER?

A) Calcium ions are actively imported from the cytoplasm into the ER.

3) Which of the following is a likely explanation of why natural selection favored the evolution of signals for sexual reproduction?

A) Even in the simplest organisms, sexual reproduction required several coordinated responses by cells.

49) In research on aging (both cellular aging and organismal aging), it has been found that aged cells do not progress through the cell cycle as they had previously. Which of the following would provide evidence that this is related to cell signaling?

A) Growth factor ligands do not bind as efficiently to receptors.

48) In C. elegans, ced-9 prevents apoptosis in a normal cell in which of the following ways?

A) It prevents the caspase activity of ced-3 and ced-4.

11) Which of the following is true for the signaling system in an animal cell that lacks the ability to produce GTP?

A) It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.

Humans have receptors for two kinds of beta adrenergic compounds such as catecholamines to control cardiac muscle contractions. Some are beta 1 receptors that promote increased heart rate. Other drugs, called beta blockers, slow heart rate. Smooth muscle cells, however, have beta 2 receptors, which mediate muscle relaxation. Blockers of these effects are sometimes used to treat asthma. 59) The description above illustrates which of the following?

A) Just because a drug acts on one type of receptor does not mean that it will act on another type.

8) In an experiment to track the movement of growth factor molecules from secretion to the point of receptor binding in a particular species of mammal, a student found a 20-fold reduction in mm traveled when in the presence of an adrenal hormone. This is in part attributable to which of the following?

A) The growth factor is a paracrine signal.

19) In general, a signal transmitted via phosphorylation of a series of proteins

A) brings a conformational change to each protein.

66) Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger.

A) cAMP

64) The activation of receptor tyrosine kinases is characterized by

A) dimerization and phosphorylation.

33) One inhibitor of cGMP is Viagra. It provides a signal that leads to dilation of blood vessels and increase of blood in the penis, facilitating erection. Since cGMP is inhibited, the signal is prolonged. The original signal that is now inhibited would have

A) hydrolyzed cGMP to GMP.

Paracrine signaling

A) involves secreting cells acting on nearby target cells by discharging a local regulator into the extracellular fluid

22) The toxin of Vibrio cholerae causes profuse diarrhea because it

A) modifies a G protein involved in regulating salt and water secretion.

24) Which of the following most likely would be an immediate result of growth factor binding to its receptor?

A) protein kinase activity

10) Of the following, a receptor protein in a membrane that recognizes a chemical signal is most similar to

A) the active site of an allosteric enzyme that binds to a specific substrate.

50) Where do apoptotic signals come from?

A) the nucleus only B) the ER only C) ligand binding only D) mitochondrial protein leakage only E) all of the above

1) Using the yeast signal transduction pathways, both types of mating cells release the mating factors. These factors bind to specific receptors on the correct cells,

A) which induce changes in the cells that lead to cell fusion.

47) Why is apoptosis potentially threatening to the healthy "neighbors" of a dying cell?

B) Lysosomal enzymes exiting the dying cell would damage surrounding cells.

7) In which of the following ways do plant hormones differ from hormones in animals?

B) Plant hormones may travel in air or through vascular systems.

Affinity chromatography is a method that can be used to purify cell-surface receptors, while they retain their hormone-binding ability. A ligand (hormone) for a receptor of interest is chemically linked to polystyrene beads. A solubilized preparation of membrane proteins is passed over a column containing these beads. Only the receptor binds to the beads. 57) When an excess of the ligand (hormone) is poured through the column after the receptor binding step, what do you expect will occur?

B) The ligand will cause the receptor to be displaced from the beads and eluted out.

44) Why has C. elegans proven to be a useful model for understanding apoptosis?

B) The nematode undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development.

16) Since steroid receptors are located intracellularly, which of the following is true?

B) The steroid/receptor complex can cross the nuclear membrane.

38) In which of the following ways could signal transduction most probably be explored in research to treat cancer?

B) alteration of protein kinases in cell cycle regulation in order to slow cancer growth

A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others. 54) Where would you expect to find the carboxyl end?

B) at the cytosol surface

12) Testosterone functions inside a cell by

B) binding with a receptor protein that enters the nucleus and activates specific genes.

Membrane receptors that attach phosphates to specific amino acids in proteins are

B) called receptor tyrosine-kinases

65) Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because

B) intracellular receptors are present only in target cells.

A small molecule that specifically binds to another molecule, usually a larger one

B) is called a ligand

Affinity chromatography is a method that can be used to purify cell-surface receptors, while they retain their hormone-binding ability. A ligand (hormone) for a receptor of interest is chemically linked to polystyrene beads. A solubilized preparation of membrane proteins is passed over a column containing these beads. Only the receptor binds to the beads. 58) This method of affinity chromatography would be expected to collect which of the following?

B) molecules of purified receptor

When the epinephrine model for signal transduction returns back to the "ground state" (after the stimulus disappears), what destroys the remaining cyclic AMP?

B) phosphodiesterase

From the perspective of the cell receiving the message, the three stages of cell signaling are

B) signal reception, signal transdcution, and cellular response

Which of the following are chemical messengers that pass through the plasma membrane of cells and have receptor molecules in the cytoplasm?

B) testosterone

The process of transduction usually begins

B) when the signal molecule changes the receptor protein in some way

32) Which of the following is a correct association?

C) GTPase activity and hydrolysis of GTP to GDP

68) Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?

C) Glycogen breakdown was observed only when epinephrine was administered to intact cells.

17) Receptor tyrosine kinases (RTKs) are found at high levels on various cancer cells. A protein, Herceptin, has been found to bind to an RTK known as HER2. This information can now be utilized in breast cancer treatment if which of the following is true?

C) If the patient's cancer cells have detectable HER2.

34) Which of the following is the best explanation for the fact that most transduction pathways have multiple steps?

C) Multiple steps provide for greater possible amplification of a signal.

In regard to cyclic AMP as second messenger, which of the following does cAMP activate?

C) Protein kinase

39) A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following?

C) a decrease in transcriptional activity of certain genes

46) If an adult person has a faulty version of the human analog to ced-4 of the nematode, which of the following is most likely to result?

C) a form of cancer in which there is insufficient apoptosis

69) Protein phosphorylation is commonly involved with all of the following except

C) activation of G protein-coupled receptors.

5) In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function?

C) aggregation of bacteria that can cause cavities

51) The human population's life expectancy has increased significantly but seems to have an upper limit. Which of the following might be described as an ecological consequence of passing that upper limit by regulating cell death?

C) an increase in the total population of humans on the planet

G proteins and G-protein-linked receptors

C) are thought to have evolved very early, because of their similar structure and function in wide variety of modern organisms.

27) Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of

C) cAMP.

In our example of cell signaling (epinephrine model), which of the following was designated as the "second messenger"?

C) cyclic AMP

Humans have receptors for two kinds of beta adrenergic compounds such as catecholamines to control cardiac muscle contractions. Some are beta 1 receptors that promote increased heart rate. Other drugs, called beta blockers, slow heart rate. Smooth muscle cells, however, have beta 2 receptors, which mediate muscle relaxation. Blockers of these effects are sometimes used to treat asthma. 60) The use of beta 2 antagonist drugs may be useful in asthma because they may

C) dilate the bronchioles by relaxing their smooth muscle.

43) GTPase activity is involved in the regulation of signal transduction because it

C) hydrolyzes GTP binding to G protein.

21) Which of the following is the best explanation for the inability of a specific animal cell to reduce the Ca2+ concentration in its cytosol compared with the extracellular fluid?

C) insufficient ATP levels in the cytoplasm

41) What are scaffolding proteins?

C) large molecules to which several relay proteins attach to facilitate cascade effects

4) Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding?

C) paracrine signaling

When a cell releases a signal molecule into the environment and a number of cells in the immediate vicinity respond, this type of signaling is

C) paracrine signaling

26) Adenylyl cyclase has the opposite effect of which of the following?

C) phosphodiesterase

35) Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction?

C) serine and threonine

Which of the following is bound to ACTIVE tyrosine kinase receptor?

C) signal

62) Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because

C) they amplify the original signal manyfold.

28) If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound

C) to block G protein activity in liver cells.

In regard to cell signaling, which of the following corresponds to the "second messenger"?

D) Cyclic AMP

40) At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogens and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects?

D) Estrogen binds to specific receptors inside many kinds of cells, each of which have different responses to its binding.

Which of the following directly activates phospholipase C?

D) G protein

Up to 60% of all medicines used today exert their effects by influencing what structures in the cell membrane?

D) G proteins

Which of the following is bound to INACTIVE G protein?

D) GDP

Synaptic signaling between adjacent neurons is like hormone signaling in which of the following ways?

D) It requires binding of a signaling molecule to a receptor

45) Which of the following describes the events of apoptosis?

D) Its DNA and organelles are fragmented, the cell shrinks and forms blebs, and the cell self-digests.

13) Which of the following is true of transcription factors?

D) They control gene expression.

2) What is most likely to happen to an animal's target cells that lack receptors for local regulators?

D) They might not be able to multiply in response to growth factors from nearby cells.

Where in the cell is the receptor of rate steroid hormone located, before it binds the hormone?

D) in the cytosol

42) The termination phase of cell signaling requires which of the following?

D) incompatibility of the binding of the signal molecule to the receptor

Humans have receptors for two kinds of beta adrenergic compounds such as catecholamines to control cardiac muscle contractions. Some are beta 1 receptors that promote increased heart rate. Other drugs, called beta blockers, slow heart rate. Smooth muscle cells, however, have beta 2 receptors, which mediate muscle relaxation. Blockers of these effects are sometimes used to treat asthma. 61) Beta 2 antagonist drugs might also be used most effectively for which of the following?

D) increasing low blood pressure

63) Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?

D) ligand-gated ion channel

67) Apoptosis involves all but which of the following?

D) lysis of the cell

30) An inhibitor of which of the following could be used to block the release of calcium from the endoplasmic reticulum?

D) phospholipase C

25) An inhibitor of phosphodiesterase activity would have which of the following effects?

D) prolong the effect of epinephrine by maintaining elevated cAMP levels in the cytoplasm

In the overview of the cell signaling, what occurs during the SIGNAL TRANSDUCTION pathway?

D) protein phosphorylations

14) One of the major categories of receptors in the plasma membrane reacts by forming dimers, adding phosphate groups, and then activating relay proteins. Which type does this?

D) receptor tyrosine kinases

18) The receptors for a group of signaling molecules known as growth factors are often

D) receptor tyrosine kinases.

Which of the substances below is a protein that can hold several other relay proteins as it binds to activated membrane receptor?

D) scaffolding protein

6) In yeast signal transduction, the yeast cells

D) secrete molecules that result in response by other yeast cells.

9) When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway?

D) signal molecule

29) If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound

D) that increases phosphodiesterase activity.

A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others. 56) If you wish to design an experiment to block the G protein-coupled receptor interaction, the block would preferentially affect which of the following?

D) the amino acid sequence in the binding site for the G protein

Which of the following powers cyclic AMP formation?

E) Adenylyl cyclase

Choose from the terms below the one that activates adenyl cyclase.

E) G-protein

Which of the following is bound to ACTIVE G protein in the epinephrine model?

E) GTP

31) Which of the following statements is true of signal molecules?

E) Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

15) Because most receptors are membrane proteins, which of the following is usually true?

E) They change their conformation after binding with signal polypeptides.

A major group of G protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others. 55) The coupled G protein most likely interacts with this receptor

E) at the loop between H5 and H6.

20) Sutherland discovered that epinephrine signals

E) elevation of cytosolic concentrations of cyclic AMP.

36) The function of phosphatases in signal transduction is best described as to

E) inactivate protein kinases and turn off the signal transduction.

23) Which of the following would be inhibited by a drug that specifically blocks the addition of phosphate groups to proteins?

E) receptor tyrosine kinase activity