Deck 9: Cellular Signaling

Question 1

Which of the following statements best explains why testosterone, a lipid-soluble signaling molecule that crosses the membranes of all cells, affects only target cells?

A) Only target cells retain the appropriate genes regulated by testosterone.
B) Only target cells contain the intracellular receptors for testosterone.
C) Only target cells possess the cytosolic enzymes that transduce the signal from testosterone to adenylyl cyclase.
D) Testosterone initiates a phosphorylation cascade only in target cells.

Answer 1

B

Question 2

Which of the following statements best describes the function of the α factor secreted by yeast cells?

A) It binds to receptors on α cells to stimulate mating between α cells.
B) It binds to receptors on α cells to stimulate mating between a cells and α cells.
C) It binds to receptors on a cells to stimulate mating between a cells.
D) It diffuses through the membranes of a cells, binds to DNA and initiates transcription of a factor genes.

Answer 2

B

Question 3

If yeast cells of mating type α with normal mating factor receptors are genetically modified to produce only mating factor a, they will mate with which of the following cells?

A) only normal mating type α cells
B) only normal mating type a cells
C) only normal mating type α cells, or with each other
D) only with each other

Answer 3

D

Question 4

Which of the following observations suggests that a second messenger is required for the activation of glycogen phosphorylase by epinephrine?

A) Glycogen phosphorylase is inactive in the absence of epinephrine in a cell-free system.
B) Glycogen breakdown occurs only when epinephrine is administered to intact cells.
C) Glycogen breakdown occurs when epinephrine and glycogen phosphorylase are combined in a cell-free system.
D) Epinephrine binds directly to glycogen phosphorylase.

Question 5

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

A) relay molecule
B) transducer
C) signal molecule
D) response molecule

Question 6

Which of the following statements describes a likely effect of a drug that inhibits testosterone binding to its receptor in human cells?

A) The cytosolic levels of cAMP would decrease.
B) The expression of certain genes would increase or decrease.
C) The cytosolic calcium concentration would increase.
D) The activity of G proteins would decrease.

Question 7

Which of the following statements best describes the effect of a mutation that alters the structure of the a factor so that it no longer binds to the corresponding receptor on α cells?

A) The α cells will fail to initiate the shape changes necessary for mating.
B) The α cells will fail to secrete the α factor.
C) The a cells will fail to initiate the shape changes necessary for mating after binding α factor.
D) The a cells will mate with other a cells rather than α cells.

Question 8

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would a coupled G protein most likely interact with this receptor?

A) at the amino end
B) at the carboxyl end
C) along the exterior margin
D) at the loop between helix 5 and helix 6

Question 9

The dots in the space between the two structures in the accompanying figure represent which of the following components of a cell signaling pathway?

A) receptor molecules
B) second messengers
C) neurotransmitters
D) hormones

Question 10

Which of the following conditions is required for a target organ to respond to a particular hormone?

A) Cells in the target organ must modify their plasma membranes to allow the hormone to enter the cytoplasm.
B) The target organ must be the same as the organ that produced the hormone.
C) The target organ must have the opposite mating type of the organ that produced the hormone.
D) The target organ must have receptors that recognize and bind the hormone molecule.

Question 11

Which of the following responses is stimulated by cell signaling the formation of biofilms?

A) formation of mating complexes
B) aggregation of bacteria
C) secretion of substances that inhibit growth of foreign bacteria
D) inhibition of quorum sensing

Question 12

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

A) Plant hormones may travel through the air as a gas.
B) Plant hormones function as only paracrine signals.
C) Plant hormones may be transported from the hormone producing cell to the responding cell through a vascular system.
D) Plant hormones typically travel from the hormone producing cell to an adjacent responding cell through gap junctions.

Question 13

If an animal cell suddenly loses the ability to produce GTP, what will most likely happen to its signaling system?

A) It will not be able to activate G proteins on the cytoplasmic side of the plasma membrane.
B) It will be able to carry out reception and transduction but would not be able to respond to a signal.
C) It will use ATP instead of GTP to activate G proteins on the cytoplasmic side of the plasma membrane.
D) It will not be able to activate receptor tyrosine kinases.

Question 14

Many G protein-coupled receptors contain seven transmembrane α-helical domains. If the amino terminus of such a protein is located on the extracellular side of the membrane, where would you expect to find the carboxyl terminus of the protein?

A) at the exterior surface of the plasma membrane
B) at the cytosolic surface of the plasma membrane
C) covalently bound to the amino end of the protein
D) embedded in the phospholipid bilayer of the membrane

Question 15

Which of the following statements best describes a key aspect of a G protein signaling pathway?

A) A G protein-coupled receptor is active when bound to GTP.
B) A G protein bound is active when bound to GTP.
C) A G protein bound is active when bound to GDP.
D) A G protein is activated by hydrolysis of bound GTP.

Question 16

Which of the following signal transduction proteins are activated by phosphorylation after binding to a signal molecule?

A) G protein-coupled receptors
B) ligand-gated ion channels
C) steroid receptors
D) receptor tyrosine kinases

Question 17

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?

A) receptor tyrosine kinase
B) G protein-coupled receptor
C) ligand-gated ion channel
D) steroid receptor

Question 18

A type of localized signaling in which a cell secretes a signal molecule that affects neighboring cells is best described as which of the following?

A) hormonal signaling
B) autocrine signaling
C) paracrine signaling
D) cell-cell contact-dependent signaling

Question 19

Which of the following signal transduction proteins typically functions by forming dimers after binding to a signal molecule?

A) G protein-coupled receptors
B) ligand-gated ion channels
C) steroid receptors
D) receptor tyrosine kinases

Question 20

Which of the following statements best describes the mechanism by which testosterone functions inside a cell?

A) It acts as a signal receptor that activates tyrosine kinases.
B) It binds with a receptor protein that enters the nucleus and activates expression of specific genes.
C) It acts as a steroid signal receptor that activates ion channel proteins in the plasma membrane.
D) It coordinates a phosphorylation cascade that reduces spermatogenesis.

Question 21

Which of the following statements best would best explain the inability of an animal cell to reduce the Ca2+ concentration in its cytosol?

A) The calcium-gated ion channels in the cell membrane are inactive.
B) Excessive amounts of calcium are transported from the cytosol into the endoplasmic reticulum.
C) Insufficient amounts of ATP are present in the cytosol.
D) Insufficient numbers of protein kinases are present in the cell.

Question 22

Activation of which of the following molecules generally requires protein phosphorylation?

A) receptor tyrosine kinases
B) steroid hormone receptors
C) G protein-coupled receptors
D) ligand-gated ion channels

Question 23

What does it mean to say that a signal is transduced?

A) The signal enters the cell directly and binds to a receptor inside.
B) The physical form of the signal changes as it passes from the cell membrane to the ultimate intracellular target.
C) The signal is amplified, such that even one signal molecule evokes a large response.
D) The signal triggers a sequence of phosphorylation events inside the cell.

Question 24

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

A) serine/threonine kinases
B) phosphodiesterase
C) phospholipase C
D) adenylyl cyclase

Question 25

Which of the following statements best describes an aspect of signal transduction?

A) When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules.
B) In response to some G protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium.
C) In most cases, signal molecules interact with the cell at the plasma membrane, enter the cell, and eventually enter the nucleus.
D) Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

Question 26

How does the toxin of Vibrio cholerae cause profuse diarrhea?

A) It modifies a G protein involved in regulating salt and water secretion.
B) It modifies adenylyl cyclase and triggers excess formation of cAMP.
C) It signals IP3 to act as a second messenger for the release of calcium.
D) It modifies a ligand-gated ion channel.

Question 27

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

A) tyrosine
B) glycine and histidine
C) serine and threonine
D) glycine and glutamic acid

Question 28

Which of the following statements best describes steroid receptors?

A) They are lipids or glycolipids.
B) They may be inside the nucleus of a target cell.
C) They are embedded in the plasma membrane.
D) They are typically bound to the external surface of the nuclear membrane.

Question 29

Certain receptor tyrosine kinases (RTKs) that promote excessive cell division are found at high levels in various cancer cells. HER2 is an RTK that is present at excessively high levels in some breast cancer cells. Herceptin is a protein that binds to HER2 and inhibits cell division. Herceptin may be an effective treatment for breast cancer treatment under which of the following conditions?

A) If injection of HER2 in the patient's cancer cells inhibits cell division.
B) If the patient's cancer cells have excessive levels of HER2.
C) If the patient lacks functional HER2 proteins.
D) If the patient has excessive levels of other RTKs in cancer cells.

Question 30

Caffeine is an inhibitor of phosphodiesterase. Therefore, the cells of a person who has recently consumed coffee would have increased levels of which of the following molecules?

A) phosphorylated proteins
B) cAMP
C) adenylyl cyclase
D) activated G proteins

Question 31

Binding of a growth factor to its receptor is most likely to immediately activate which of the following molecules?

A) protein kinase
B) adenylyl cyclase
C) cAMP
D) phosphorylase

Question 32

A signal transmitted via phosphorylation of a series of proteins is generally associated with which of the following events?

A) conformational changes to each protein in the series
B) binding of a hormone to an intracellular receptor
C) activation of a ligand-gated ion channel
D) production of ATP in the process of signal transduction

Question 33

Which of the following statements best describes the relationship between an enzyme and its function?

A) kinase: addition of a tyrosine
B) phosphodiesterase: removal of phosphate groups
C) GTPase: hydrolysis of GTP
D) adenylyl cyclase: conversion of cAMP to AMP

Question 34

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

A) binding of G proteins to G protein-coupled receptors
B) ligand-gated ion channel signaling pathways
C) adenylyl cyclase activity
D) receptor tyrosine kinase activity

Question 35

A protein kinase is an enzyme that functions in which of the following ways?

A) by serving as a second messenger molecule
B) by serving as a receptor for various signal molecules
C) by adding a phosphate group to activate or inactivate other proteins
D) by activating a G protein

Question 36

What role do phosphatases play in signal transduction pathways?

A) They transfer a phosphate group from one protein in the pathway to the next molecule in the series.
B) They activate protein kinases by phosphorylation.
C) They amplify the second messenger cAMP.
D) They inactivate protein kinases to turn off signal transduction.

Question 37

Which of the following enzymes essentially reverses the reaction catalyzed by adenylyl cyclase?

A) protein kinase
B) protein phosphatase
C) phosphodiesterase
D) phosphorylase

Question 38

Which of the following statements best describes how steroid hormones access their receptors within target cells?

A) Steroid hormone receptors undergo conformational changes that relocate them on the membrane surface.
B) Both steroid hormones and their receptors are produced by the same cells.
C) Steroid hormones are lipid soluble, so they can readily diffuse through the lipid bilayer of the cell and nuclear membranes.
D) Steroid hormones first bind to a steroid activator and this complex is transported across the cell membrane by a steroid transport protein.

Question 39

Not all intercellular signals require transduction. Which one of the following signals may be processed without transduction?

A) a lipid-soluble signal
B) a signal that is weakly bound to a nucleotide
C) a signal that binds to a receptor in the cell membrane
D) a signal that binds to the extracellular matrix

Question 40

Viagra causes dilation of blood vessels and increased blood flow to the penis, which helps to maintain an erection. Viagra acts by inhibiting which of the following events?

A) hydrolysis of cGMP to GMP
B) hydrolysis of GTP to GDP
C) dephosphorylation of cGMP
D) formation of cGMP from GTP

Question 41

Which of the following statements best describes a typical cAMP-mediated signal transduction event?

A) The second messenger is the last part of the system to be activated.
B) A hormone activates the second messenger by directly binding to it.
C) The second messenger amplifies the hormonal response by attracting more hormones to the cell being affected.
D) Adenylyl cyclase is activated after the hormone binds to the cell and before phosphorylation of proteins occurs.

Question 42

A drug could inhibit the release of glucose from liver cells by having which of the following effects on the liver cells?

A) activating epinephrine receptors
B) increasing cAMP production
C) blocking G protein activity
D) increasing glycogen phosphorylase activity

Question 43

Which of the following statements best describes the events of apoptosis?

A) The cell dies, it is lysed, its organelles are phagocytized, and its contents are recycled.
B) The cell's DNA and organelles become fragmented, the cell dies, and it is phagocytized.
C) The cell's DNA and organelles become fragmented, the cell shrinks and forms blebs, and the cell's parts are packaged in vesicles that are digested by specialized cells.
D) The cell's nucleus and organelles are lysed, and then the cell enlarges and bursts.

Question 44

Consider the following pathway:
Epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP
Which of the following molecules serves as the second messenger in this pathway?

A) cAMP
B) G protein
C) adenylyl cyclase
D) G protein-coupled receptor

Question 45

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

A) intracellular receptor
B) G protein-coupled receptor
C) phosphorylated receptor tyrosine kinase dimer
D) ligand-gated ion channel

Question 46

Which of the following occurs during apoptosis?

A) lysis of the cell
B) direct contact between signaling cells
C) fragmentation of the DNA
D) release of proteases outside the cell

Question 47

A loss of function of Apaf1, the human homologue of ced-4 in nematodes, is most likely to result in which of the following?

A) activation of a developmental pathway found in the nematode but not in humans
B) a form of cancer in which normal apoptosis fails
C) excess activation of the human analog of the ced-3 protease
D) extensive tissue damage due to excess apoptosis

Question 48

Binding of epinephrine to its receptor results in which of the following events?

A) Stimulation of glycogen synthesis.
B) A decrease in blood glucose levels.
C) Inhibition of glycogen phosphorylase.
D) Elevation of cytosolic concentrations of cyclic AMP.

Question 49

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

A) cAMP
B) G protein
C) GTP
D) adenylyl cyclase

Question 50

Which of the following statements best describes the mechanism by which the ced-9 protein in the nematode C. elegans prevents apoptosis in normal cells?

A) Active ced-9 prevents activation of the caspase activity of ced-3.
B) Ced-9 remains inactive until it is stimulated by ced-3 and other caspases.
C) Ced-9 is cleaved to produce the active ced-3 caspase.
D) Ced-9 inhibits the cell membrane receptor for the death-signaling molecule.

Question 51

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because ________.

A) only target cells retain the appropriate DNA segments
B) intracellular receptors are present only in target cells
C) only target cells have enzymes that break down aldosterone
D) only in target cells is aldosterone able to initiate the phosphorylation cascade that turns genes on

Question 52

Which of the sequences below best describes the sequential steps (numbered 1-5) in a signal transduction pathway that utilizes a G protein-coupled receptor?
1) The signal-receptor complex activates a G protein.
2) Protein kinases are activated.
3) A signal molecule binds to a receptor.
4) Target proteins are phosphorylated.
5) cAMP is produced.

A) 1, 2, 3, 4, 5
B) 3, 1, 2, 4, 5
C) 3, 1, 5, 2, 4
D) 1, 2, 5, 3, 4

Question 53

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

A) Estrogen is produced in very large concentration by nearly every tissue of the body.
B) Each cell responds in the same way when steroids bind to the cell surface.
C) Estrogen is kept away from the surface of any cells, not able to bind it at the surface.
D) Estrogen binds to specific receptors inside many kinds of cells, each with different responses.

Question 54

Which of the following statements best describes scaffolding proteins?

A) microtubule arrays that allow lipid-soluble hormones to get from the cell membrane to the nuclear pores
B) large molecules to which several relay proteins attach to facilitate cascade effects
C) relay proteins that orient receptors and their ligands in appropriate directions to facilitate complex formation
D) proteins that enter the nucleus of a cell to regulate transcription

Question 55

The activation of receptor tyrosine kinases is characterized by ________.

A) dimerization and phosphorylation
B) dimerization and IP3 binding
C) a phosphorylation cascade
D) GTP hydrolysis

Question 56

Which of the following statements best describes a reason that C. elegans is an excellent model organism for investigating apoptosis?

A) Cells in C. elegans do not naturally undergo apoptosis, but can be induced to do so in the laboratory.
B) C. elegans undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development.
C) C. elegans has large cells wherein apoptosis is easily observed without the aid of a microscope.
D) Death in C. elegans through a well-defined sequence of apoptotic events.

Question 57

What is a primary function of transcription factors?

A) They regulate the synthesis of DNA in response to a signal.
B) They convert ATP into cAMP.
C) They control gene expression.
D) They regulate the release of calcium from the endoplasmic reticulum.

Question 58

Which of the following statements best describes why phosphorylation cascades are useful in cellular signal transduction?

A) they are species specific
B) they always lead to the same cellular response
C) they amplify the original signal many times
D) they counter the harmful effects of phosphatases

Question 59

Some cases of human melanoma have been shown to result from inhibition of apoptosis in these cells. The human analogue of which of the following defects in C. elegans could cause these cancers?

A) A ced-9 protein that is always inactive.
B) A ced-3 protein that is always inactive.
C) A ced-4 protein that is always active.
D) A death-signaling molecule receptor that is always active.

Question 60

Which of the following statements best describes the effect of a mutation that knocks out the GTPase activity of a G protein?

A) The concentration of available GTP would decrease.
B) The number of G proteins in the cell would increase.
C) The G protein would be inactivated by a G protein-coupled receptor/signal molecule complex.
D) The G protein would always be active.

Question 61

Protein phosphorylation is commonly involved with which of the following?

A) ligand binding by receptor tyrosine kinases
B) activation of G protein-coupled receptors
C) activation of protein kinase molecules
D) release of Ca2+ from the ER lumen

Question 62

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

A) Enzymatic activity was proportional to the amount of calcium added to a cell-free extract.
B) Receptor studies indicated that epinephrine was a ligand.
C) Glycogen breakdown was observed only when epinephrine was administered to intact cells.
D) Glycogen breakdown was observed only when epinephrine and glycogen phosphorylase were mixed.