1) In yeast signal transduction, a yeast cell releases a mating factor, which ________.
A) acts back on the same cell that secreted the mating factor, changing its development
B) passes through the membranes of neighboring cells, binds to DNA, and initiates transcription C) binds to receptors on the membranes of other types of yeast cells
D) diffuses through the membranes of distant cells, causing them to produce factors that initiate long-distance migrations

C

Yeast cells of mating type a are genetically engineered to produce only mating factor α instead of the normal mating factor a. The gene for the mating factor receptor was unaltered. How will these engineered cells behave in terms of mating?
A) They will only mate with normal mating type a cells.

B) They will only mate with normal mating type α cells.
C) They will mate with each other or with normal mating type a cells, but not with normal mating type α cells.
D) They will only mate each other and not with normal mating type a or α cells.

C

In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function?
A) formation of mating complexes
B) aggregation of bacteria that can cause cavities

C) secretion of substances that inhibit foreign bacteria D) digestion of unwanted parasite populations

B

Which of the following is a type of local signaling in which a cell secretes a signal molecule that affects neighboring cells?
A) hormonal signaling
B) autocrine signaling

C) paracrine signaling
D) synaptic signaling

C

Hormones are chemical substances produced in one organ that are released into the bloodstream and affect the function of a target organ. Which of the following conditions is required for the 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.

D

In which of the following ways do plant hormones differ from hormones in animals? A) Plant hormones frequently travel through the air as a gas.
B) Animal hormones are only local regulators.
C) Plant hormones commonly travel through the soil from one plant to another.

D) Animal hormones typically travel from the hormone producing cell to an adjacent responding cell through gap junctions.

A

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

C

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?
A) Receptor studies indicated that epinephrine was a ligand.
B) Glycogen breakdown was observed only when epinephrine was administered to intact cells. C) Glycogen breakdown was observed when epinephrine and glycogen phosphorylase were combined in a cell-free system.

D) Epinephrine was known to have different effects on many types of cells.

B

Which of the following statements about a G protein signaling pathway is true? A) A G protein-coupled receptor bound to GTP is in its active state.
B) A G protein bound to GTP is in its active state.
C) A G protein bound to GDP is in its active state.

D) Hydrolysis of bound GTP by a G protein activates the G protein.

B

What is the most likely 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.

B

Scientists have found that extracellular matrix components may induce specific gene expression in embryonic tissues such as the liver and testes. For this to happen, there must be direct communication between the extracellular matrix and the developing cells. Which kind of transmembrane protein would most likely be involved in this kind of induction?
A) integrins
B) fibronectins
C) actin microfilaments
D) receptor tyrosine kinases

A

One of the major categories of receptors in the plasma membrane functions by forming dimers, adding phosphate groups, and then activating relay proteins. Which type does this? A) G protein-coupled receptors
B) ligand-gated ion channels

C) steroid receptors
D) receptor tyrosine kinases

D

Which of the following statements describes a likely effect of a drug designed that inhibits the cellular response to testosterone?
A) The cytoplasmic levels of cAMP would decrease.
B) The transcription of certain genes would decrease.

C) The cytosolic calcium concentration would increase. D) The activity of G proteins would decrease.

B

Many G protein-coupled receptors contain seven transmembrane α-helical domains. 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 surface or on the cytosolic surface of the membrane. The loop on the cytosolic side between helices 5 and 6 is usually substantially longer than the others. Where would you expect to find the carboxyl end of the protein?

A) at the exterior surface
B) at the cytosolic surface
C) connected with the loop at H5 and H6
D) embedded in the phospholipid bilayer of the membrane

B

Many G protein-coupled receptors contain seven transmembrane α-helical domains. 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 surface or on the cytosolic surface of the membrane. The loop on the cytosolic side between helices 5 and 6 is usually substantially longer than the others. 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 H5 and H6

D

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

C

Why does testosterone, a lipid-soluble signaling molecule that crosses the membranes of all cells, affect only target cells?
A) Only target cells retain the appropriate genes regulated by testosterone.
B) Intracellular receptors for testosterone are present only in target cells.

C) Only target cells possess the cytosolic enzymes that transduce the signal from testosterone to adenylyl cyclase.
D) Only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor.

B

If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system?
A) It would not be able to activate G proteins on the cytoplasmic side of the plasma membrane. B) It would be able to carry out reception and transduction but would not be able to respond to a signal.

C) It would use ATP instead of GTP to activate G proteins on the cytoplasmic side of the plasma membrane.
D) It would not be able to activate receptor tyrosine kinases.

A

Which of the following statements is true of steroid receptors?
A) The receptor molecules are themselves lipids or glycolipids.
B) The receptor may be inside the nucleus of a target cell.
C) The unbound steroid receptors are quickly recycled by lysosomes.

B

Particular 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 stimulates cell division. B) If the patient's cancer cells have excessive levels of HER2.
C) If the patient's genome codes for the HER2.
D) If the patient has excessive levels of other RTKs in cancer cells.

B

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

D

The receptors for steroid hormones are located inside the cell instead of the membrane surface like most other signal receptors. How do steroids gain access to their receptors? 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 membrane.
D) Steroid hormones first bind to a steroid activator and this complex is transported across the cell membrane by a steroid transport protein.

C

Not all intercellular signals require transduction. Which one of the following signals would 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

A

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.

B

Which of the following processes generally requires protein phosphorylation? A) activation of receptor tyrosine kinases
B) activation of steroid hormone receptors
C) activation of G protein-coupled receptors

D) activation ligand-gated ion channels

A

) 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

A

Which of the following is the most plausible explanation for why an animal cell would be

unable to reduce the Ca2+ concentration in its cytosol compared with the extracellular fluid? A) inactivation of calcium-gated ion channels in the cell membrane
B) excessive transport of calcium from the cytosol into the endoplasmic reticulum
C) insufficient ATP levels in the cytosol

D) insufficient levels of protein kinase in the cell

C

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.

A

Which of the following results would most likely be an immediate result of a growth factor binding to its receptor?
A) protein kinase activity
B) adenylyl cyclase activity

C) cAMP activity
D) phosphorylase activity

A

The activity of adenylyl cyclase is essentially the opposite of which of the following enzymes?
A) protein kinase
B) protein phosphatase

C) phosphodiesterase
D) phosphorylase

C

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

B

) 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

C

Which of the following statements is true of signal molecules?
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.

D

Which of the following is a correct association?
A) kinase activity and the addition of a tyrosine
B) phosphodiesterase activity and the removal of phosphate groups C) GTPase activity and hydrolysis of GTP to GDP
D) adenylyl cyclase activity and the conversion of cAMP to AMP

C

Protein kinase is an enzyme that functions in which of the following ways? A) as a second messenger molecule
B) as a receptor for various signal molecules
C) activates or inactivates other proteins by adding a phosphate group to them D) activates a G protein

C

Viagra causes dilation of blood vessels and increased blood flow to the penis, facilitating 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

A

Which of the following amino acids are most frequently phosphorylated by protein kinases in the cytoplasm during signal transduction?
A) tyrosines
B) glycine and histidine

C) serine and threonine
D) glycine and glutamic acid

C

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.

D

If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound that does which of the following?
A) activates epinephrine receptors in liver cells
B) increases cAMP production in liver cells

C) blocks G protein activity in liver cells
D) increases glycogen phosphorylase activity in liver cells

C

If a pharmaceutical company wished to design a drug to maintain low blood sugar levels, one approach might be to design a compound that does which of the following?
A) increases glycogen phosphorylase activity in liver cells
B) activates adenylyl cyclase in liver cells

C) stimulates G protein activity in liver cells
D) increases phosphodiesterase activity in liver cells

D

Consider this pathway:
epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP

The second messenger in this pathway is ________. A) cAMP
B) G protein
C) adenylyl cyclase

D) G protein-coupled receptor

A

Sutherland discovered that the signaling molecule epinephrine is responsible for which of the following events?
A) Stimulating glycogen synthesis.
B) Decreasing blood glucose levels.

C) Interacting directly with glycogen phosphorylase. D) Elevating cytosolic concentrations of cyclic AMP.

D

Which of the following is true during 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.

D

Put the steps of the process of signal transduction in the order they occur.

1. A conformational change in the signal-receptor complex activates an enzyme.
2. Protein kinases are activated.
3. A signal molecule binds to a receptor.
4. Target proteins are phosphorylated.
5. Second messenger molecules are released.

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

C

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.

C

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 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.

D

What are 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

B

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because they ________.
A) are species specific
B) always lead to the same cellular response

C) amplify the original signal many times
D) counter the harmful effects of phosphatases

C

A mutation that knocks out the GTPase activity of a G protein would have what effect on a cell?
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.

D

Why has C. elegans proven to be a useful model for understanding apoptosis?
A) C. elegans does not naturally use 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) As C. elegans ages, its cells die progressively until the whole organism is dead.

B

Which of the following statements 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.

C

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?
A) activation of a developmental pathway found in the worm but not in humans
B) a form of cancer in which there is insufficient apoptosis

C) formation of molecular pores in the mitochondrial outer membrane D) excess skin loss

B

n the nematode 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.
B) Ced-9 remains inactive until it is signaled by ced-3 and other caspases.

C) Ced-9 cleaves to produce ced-3 and ced-4.
D) Ced-9 prevents blebbing by its action on the cell membrane.

A

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, if found in cells or organisms as they age, would provide evidence that this is related to cell signaling?

A) Growth factor ligands do not bind as efficiently to receptors. B) Hormone concentrations decrease.
C) cAMP levels change very frequently.
D) Enzymatic activity declines.

A

Which of the following provides the best evidence that cell-signaling pathways evolved early in the history of life?
A) Cell-signaling pathways are seen in "primitive" cells such as bacteria and yeast.
B) Bacteria and yeast cells signal each other in a process called quorum sensing.

C) Signal transduction molecules identified in distantly related organisms are similar. D) Most signals in all types of cells are received by cell surface receptors.

C

Cells that are infected, damaged, or have reached the end of their functional life span often undergo "programmed cell death." This controlled cell suicide is called apoptosis. Select the appropriate description of this event on a cell's life cycle.
A) Apoptosis is regulated by cell surface receptors that signal when a cell has reached its density-dependent limits.

B) During apoptosis, dying cells leak out their contents, including digestive enzymes that also destroy healthy cells.
C) During apoptosis, cellular agents chop up the DNA and fragment the organelles and other cytoplasmic components of a cell.

D) Each cell organelle has protein signals that initiate the breakdown of the organelle's components, which leads to cell death.

C

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

D

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.

A

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.

B

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclasec → AMP. Identify the second messenger.
A) cAMP
B) G protein

C) GTP
D) adenylyl cyclase

A

Apoptosis involves all but which of the following?

A) fragmentation of the DNA
B) cell-signaling pathways
C) lysis of the cell

D) digestion of cellular contents by scavenger cells

C

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.

C

Protein phosphorylation is commonly involved with all of the following except A) activation of receptor tyrosine kinases.
B) activation of protein kinase molecules.
C) activation of G protein-coupled receptors.

D) regulation of transcription by signaling molecules.

C