Cell Bio Final Exam - Quiz Notes

Which steps in muscle contraction require Ca2+? Question options: A) release of Acetylcholine from motor neuron B) shifting of tropomyosin to expose active sites on actin C) synthesis of Acetylcholine D) propagation of action potential E) A and B F) B and C

A and B A) release of Acetylcholine from motor neuron B) shifting of tropomyosin to expose active sites on actin

Which of the following statements about cancer is false? Question options: a) A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell. b) Chemical carcinogens cause cancer by changing the nucleotide sequence of DNA. c) Tobacco use is responsible for more than 20% of all cancer deaths. d) Viruses cause some cancers.

A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell.

Which of the following genetic changes cannot convert a proto-oncogene into an oncogene? Question options: a) A mutation in the promoter of the proto-oncogene, causing the normal protein to be transcribed and translated at an abnormally high level. b) A mutation that introduces a stop codon immediately after the codon for the initiator methionine. c) A mutation within the coding sequence that makes the protein hyperactive. d) An amplification of the number of copies of the proto-oncogene, causing overproduction of the normal protein.

A mutation that introduces a stop codon immediately after the codon for the initiator methionine.

How are phospholipid molecules that make up the surface membrane of a cell organized? Question options: a) A two-layered structure is formed, with the hydrophobic heads facing in to each other, sandwiched between the hydrophilic tails on the outside that face interior of the cell and the exterior environment. b) Both the second and fourth answer choices are possible. c) A single-layered structure is formed, with the hydrophobic heads facing in to the interior of the cell and the hydrophobic tails on the outside, facing the exterior environment. d) A single-layered structure is formed, with the hydrophobic tails facing in to the interior of the cell and the hydrophobic head on the outside, facing the exterior environment. e) A two-layered structure is formed, with the hydrophobic tails facing in to each other, sandwiched between the hydrophilic heads that face the interior of the cell and the exterior environment.

A two-layered structure is formed, with the hydrophobic tails facing in to each other, sandwiched between the hydrophilic heads that face the interior of the cell and the exterior environment.

The Nernst equation can be used to calculate the membrane potential based on the ratio of the outer and inner ion concentration. In a resting cell, membrane potential is calculated taking only K+ ions into account. What is Vwhen Co = 15 mM and Ci = 106 mM? Question options: a) 52.7 mV b) -5.3 mV c) -52.7 mV d) 438.1 mV

-52.7 mV

Compared to the normal situation, in which actin monomers carry ATP, what do you predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments? Question options: a) Actin filaments would grow shorter because depolymerization would be enhanced. b) No change, as addition of monomers binding nonhydrolyzable ATP would not affect actin filament length. c) Actin filaments would grow longer. d) Actin filaments would grow shorter because new monomers could not be added to the filaments.

Actin filaments would grow longer.

Which of the following statements about the unfolded protein response (UPR) is false? Question options: a) Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins. b) Activation of the UPR results in the production of more chaperone proteins. c) Activation of the UPR results in the production of more ER membrane. d) Activation of the UPR results in the cytoplasmic activation of gene regulatory proteins.

Activation of the UPR occurs when receptors in the cytoplasm sense misfolded proteins.

You are studying a signaling pathway. You know that it involves an RTK, ras, and a protein you have named Bop. You want to know if Bop acts before or after ras in the pathway. You take cells with nonfunctional Bop and expose them to the signal molecule. As you expect, the cells behave as if they do not receive the signal. You then take cells with constitutively active ras and nonfunctional Bop and observe them. They appear to not receive the signal even though ras is constitutively active. Where does Bop function in the pathway? Question options: a) Bop functions before ras b) Bop functions after ras c) it can't be determined from this type of experiment

Bop functions after ras

Figure Q16-61 shows that intracellular signaling pathways can be highly interconnected.Figure Q16-61From the information in Figure Q16-61, which of the following statements is incorrect? Question options: a) The GPCR and the RTK both activate phospholipase C. b) Activation of either the GPCR or the RTK will lead to activation of transcriptional regulators. c) CaM-kinase is only activated when the GPCR is active and not when the RTK is active. d) Ras is activated only when the RTK is active and not when the GPCR is active.

CaM-kinase is only activated when the GPCR is active and not when the RTK is active.

We can track the movement of proteins in the cell membrane by Question options: Western blot. SDS-PAGE. FRAP. none of these.

FRAP

How does S-Cdk help guarantee that replication occurs only once during each cell cycle? Question options: a) It phosphorylates and inactivates DNA helicase. b) It phosphorylates the Cdc6 protein, marking it for destruction. c) It promotes the assembly of a prereplicative complex. d) It blocks the rise of Cdc6 concentrations early in G1.

It phosphorylates the Cdc6 protein, marking it for destruction.

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant inside a typical mammalian cell? Question options: a) K+ b) Cl- c) Ca2+ d) Na+

K+

Which of the following statements about kinetochores is true? Question options: a) Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules. b) Kinetochores assemble onto chromosomes during late prophase. c) Kinetochores assemble on chromosomes that lack centromeres. d) Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome.

Kinetochores assemble onto chromosomes during late prophase.

APC is a tumor suppressor and acts in the Wnt signaling pathway to prevent the TCF complex from turning on Wnt-responsive genes. Mice that lack the gene encoding TCF4 do not have the ability to maintain the pool of proliferating gut stem cells needed to renew the gut lining. What do you predict will happen in mice that lack the APC gene? Question options: a) Mice lacking the APC gene will have a hyperactive Wnt receptor even though there is no Wnt signal. b) Mice lacking the APC gene will be like the mice lacking TCF4 and not be able to renew the gut lining. c) Mice lacking the APC gene will be like normal healthy mice, since APC is a tumor suppressor and thus not needed unless there is a tumor present. d) Mice lacking the APC gene will have inappropriate proliferation of gut stem cells.

Mice lacking the APC gene will have inappropriate proliferation of gut stem cells.

Which of the following statements about the function of the centrosome isfalse? Question options: a) Centrosomes contain hundreds of copies of the g-tubulin ring complex important for microtubule nucleation. b) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome. c) Centrosomes are the major microtubule-organizing center in a cells. d) Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules.

Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.

Which of the following statements about microtubules is true? Question options: a) ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule. b) Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell. c) The centromere nucleates the microtubules of the mitotic spindle. d) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.

Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.

You discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is ________________. Question options: a) MtA binds to GTP-bound tubulin on microtubules. b) MtA is involved in stabilizing microtubules. c) MtA is important for the interaction of microtubules with the centrosome. d) MtA will not bind to purified microtubules in a test tube.

MtA binds to GTP-bound tubulin on microtubules.

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant outside a typical mammalian cell? Question options: a) Ca2+ b) Na+ c) Cl- d) K+

Na+

Your friend works in a biotechnology company and has discovered a drug that blocks the ability of Ran to exchange GDP for GTP. What is the most likely effect of this drug on nuclear transport? Question options: a) Nuclear transport receptors would be unable to release their cargo in the nucleus. b) Nuclear transport receptors would be unable to bind cargo. c) Nuclear transport receptors would interact irreversibly with the nuclear pore fibrils. d) Nuclear transport receptors would be unable to enter the nucleus.

Nuclear transport receptors would be unable to release their cargo in the nucleus.

Different glycoproteins can have a diverse array of oligosaccharides. Which of the statements below about this diversity is true? Question options: a) Different oligosaccharides are covalently linked to proteins in the ER and the Golgi. b) Extensive modification of oligosaccharides occurs in the extracellular space. c) Oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER. d) A diversity of oligosaccharyl transferases recognizes specific protein sequences, resulting in the linkage of a variety of oligosaccharides to proteins.

Oligosaccharide diversity comes from modifications that occur in the ER and the Golgi of the 14-sugar oligosaccharide added to the protein in the ER.

Which of the following statements is true? Question options: a) MAP kinase is important for phosphorylating MAP kinase kinase. b) PI 3-kinase phosphorylates a lipid in the plasma membrane. c) STAT proteins phosphorylate JAK proteins, which then enter the nucleus and activate gene transcription. d) Ras becomes activated when an RTK phosphorylates its bound GDP to create GTP.

PI 3-kinase phosphorylates a lipid in the plasma membrane.

______ are the most abundant molecules in the plasma membrane. Question options: Glycolipids Phospholipids Prostaglandins Proteins Cholesterol molecules

Phospholipids

Which of the following statements about the endoplasmic reticulum (ER) isfalse? Question options: a) The ER is the major site for new membrane synthesis in the cell. b) Proteins to be delivered to the ER lumen are synthesized on smooth ER. c) Steroid hormones are synthesized on the smooth ER. d) The ER membrane is contiguous with the outer nuclear membrane.

Proteins to be delivered to the ER lumen are synthesized on smooth ER.

Which of the following statements about the endoplasmic reticulum (ER) isfalse? Question options: a) The ER membrane is contiguous with the outer nuclear membrane. b) The ER is the major site for new membrane synthesis in the cell. c) Proteins to be delivered to the ER lumen are synthesized on smooth ER. d) Steroid hormones are synthesized on the smooth ER.

Proteins to be delivered to the ER lumen are synthesized on smooth ER.

What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only? Question options: a) The cells produced would get smaller and smaller. b) Cells would not be able to replicate their DNA. c) Cells would get larger and larger. d) The mitotic spindle could not assemble.

The cells produced would get smaller and smaller.

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? Question options: a) 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. b) The cells you create will run out of the GTP necessary to activate Ras. c) The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras. d) The cells you create will divide more frequently compared to normal cells in response to the extracellular signals that typically activate Ras

The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras.

Which of the following statements about skeletal muscle contraction is false? Question options: a) During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments. b) A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament. c) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction. d) When a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane.

The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction.

Which of the following statements about G-protein-coupled receptors (GPCRs) is false? Question options: a) GPCRs are used in endocrine, paracrine, and neuronal signaling. b) GPCRs are the largest family of cell-surface receptors in humans. c) The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains. d) GPCRs are found in yeast, mice, and humans.

The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains.

Figure Q15-34 shows the organization of a protein that normally resides in the plasma membrane. Box 1 represents an internal start-transfer sequence with positively charged residues AFTER the sequence (at the arrow) and box 2 represents another start transfer sequence. Figure Q15-34 Question options: a) The N-terminus of this protein is cytoplasmic. b) The C-terminus of this protein is cytoplasmic. c) The mature version of this protein will span the membrane twice, with both the N- and C-terminus in the lumen of the ER. d) None of the above.

The mature version of this protein will span the membrane twice, with both the N- and C-terminus in the lumen of the ER.

Which of the following statements is true? Question options: a) The mitotic spindle is largely made of intermediate filaments. b) The contractile ring divides the nucleus in two. c) The mitotic spindle helps segregate the chromosomes to the two daughter cells. d) The contractile ring is made largely of microtubules and actin filaments.

The mitotic spindle helps segregate the chromosomes to the two daughter cells.

Which of the following events does not usually occur during interphase? Question options: a) Cells grow in size. b) The centrosomes are duplicated. c) The nuclear envelope breaks down. d) DNA is replicated.

The nuclear envelope breaks down.

Which of the following statements does not accurately describe the events involved in the propagation of an action potential? Question options: a) Local depolarization causes nearby Na+ channels to open. b) Channels in depolarized regions of the membrane are inactivated until the resting membrane potential is reestablished. c) The opening of transmitter-gated K+ channels helps to repolarize the membrane. d) An initial influx of Na+ through a small cluster of channels causes local depolarization of the membrane.

The opening of transmitter-gated K+ channels helps to repolarize the membrane.

When using the Nernst equation to calculate membrane potential, we are making several assumptions about conditions in the cell. Which of the following is not a good assumption? Question options: a) K+ is the principal positive ion in the cell. b) At rest, the interior of the cell is more negatively charged than the exterior. c) The plasma membrane is primarily permeable to Na+. d) The temperature is 37°C.

The plasma membrane is primarily permeable to Na+.

The following happens when a G-protein-coupled receptor activates a G protein. Question options: a) It activates the α subunit and inactivates the βγ complex. b) The α subunit exchanges its bound GDP for GTP. c) The GDP bound to the α subunit is phosphorylated to form bound GTP. d) The β subunit exchanges its bound GDP for GTP.

The α subunit exchanges its bound GDP for GTP.

Figure Q16-18 shows the pathway through which nitric oxide (NO) triggers smooth muscle relaxation in a blood-vessel wall. Which of the following situations would lead to relaxation of the smooth muscle cells in the absence of acetylcholine?Figure Q16-18 Question options: a) a muscle cell that has cyclic GMP phosphodiesterase constitutively active b) a smooth muscle cell that has a defect in guanylyl cyclase such that it cannot bind NO c) a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP d) a drug that blocks an enzyme involved in the metabolic pathway from arginine to NO

a muscle cell that has a defect in guanylyl cyclase such that it constitutively converts GTP to cyclic GMP

Figure Q16-63 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? a) addition of a drug that blocks Y from interacting with its target b) addition of a drug that increases the affinity of protein Y and Ras c) addition of a drug that increases the activity of protein Y d) addition of a drug that prevents protein X from activating Ras

a) addition of a drug that blocks Y from interacting with its target

Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called _____________. Question options: a) facilitated diffusion. b) active transport. c) free diffusion. d)passive transport.

active transport.

Which of the following conditions is likely to decrease the likelihood of skeletal muscle contraction? Question options: a) partial depolarization of the T-tubule membrane, such that the resting potential is closer to zero b) a mutation in tropomyosin that decreases its affinity for the actin filament c) an increase in the amount of ATP in the cell d) addition of a drug that blocks Ca2+ binding to troponin

addition of a drug that blocks Ca2+ binding to troponin

Membrane proteins can function as Question options: anchors receptors enzymes transporters and channels all of these

all of these

Figure Q17-52 shows the leading edge of a lamellipodium. Which of the following statements is true?Figure Q17-52 Question options: a) There is more ATP-bound actin at the leading edge than in the actin filaments away from the leading edge. b) Nucleation of new filaments near the leading edge pushes the plasma membrane forward. c) all of these are true d) ARP proteins nucleate the branched actin filaments in the lamellipodium.

all of these are true

The hydrolysis of GTP to GDP carried out by tubulin molecules ________________. Question options: a) allows the behavior of microtubules called dynamic instability. b) occurs because the pool of free GDP has run out. c) tips the balance in favor of microtubule assembly. d) provides the energy needed for tubulin to polymerize.

allows the behavior of microtubules called dynamic instability.

Protein domains that pass through the plasma membrane can have Question options: A) alpha helices B) beta sheets arranged in a barrel C) disulfide bonds D) either A or B

alpha helices beta sheets arranged in a barrel either A or B

When introduced into mitotic cells, which of the following is expected to impair anaphase B but not anaphase A? Question options: a) an antibody against the motor proteins that move from the plus end of microtubules to the minus end b) an antibody against the motor proteins that move from the minus end of microtubules toward the plus end c) ATP gS, a nonhydrolyzable ATP analog that binds to and inhibits ATPases d) an antibody against myosin

an antibody against the motor proteins that move from the minus end of microtubules toward the plus end

Condensins ________________. Question options: a) are involved in holding sister chromatids together. b) assemble into complexes on the DNA when phosphorylated by M-Cdk. c) bind to DNA before DNA replication begins. d) are degraded when cells enter M phase.

assemble into complexes on the DNA when phosphorylated by M-Cdk.

Which of the following precede the re-formation of the nuclear envelope during M phase in animal cells? Question options: a) assembly of the contractile ring b) decondensation of chromosomes c) reassembly of the nuclear lamina d) transcription of nuclear genes

assembly of the contractile ring

In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated? Question options: a) at the end of G2 b) during M c) at the transition between G1 and S d) when cells enter G0

at the end of G2

Most proteins destined to enter the endoplasmic reticulum _________. Question options: a) are transported across the membrane after their synthesis is complete. b) are synthesized on free ribosomes in the cytosol. c) begin to cross the membrane while still being synthesized. d) remain within the endoplasmic reticulum.

begin to cross the membrane while still being synthesized.

Most proteins destined to enter the endoplasmic reticulum _________. Question options: a) remain within the endoplasmic reticulum. b) are transported across the membrane after their synthesis is complete. c) are synthesized on free ribosomes in the cytosol. d) begin to cross the membrane while still being synthesized.

begin to cross the membrane while still being synthesized.

Programmed cell death occurs ________________. Question options: a) rarely and selectively only during animal development. b) by means of an intracellular suicide program. c) only in unhealthy or abnormal cells. d) only during embryonic development.

by means of an intracellular suicide program.

Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential? Question options: a) by closing Na+ channels b) by opening Cl- channels c) by opening Ca+ channels d) by preventing the secretion of excitatory neurotransmitters

by opening Cl- channels

For both actin and microtubule polymerization, nucleotide hydrolysis is important for ______. Question options: a) increasing the rate at which subunits are added to the filaments. b) promoting nucleation of filaments. c) decreasing the binding strength between subunits on filaments. d) stabilizing the filaments once they are formed.

decreasing the binding strength between subunits on filaments.

Which of the following mechanisms is not directly involved in inactivating an activated RTK? Question options: a) dephosphorylation by serine/threonine phosphatases b) removal of the RTK from the plasma membrane by endocytosis c) dephosphorylation by protein tyrosine phosphatases d) digestion of the RTK in lysosomes

dephosphorylation by serine/threonine phosphatases

When studying a particular membrane protein, it can be removed from the membrane by adding Question options: acid. base. detergent. urea.

detergent

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________. Question options: a) activating a G protein. b) diffusing into cells and stimulating the cyclase directly. c) activating an intracellular protein kinase. d) activating a receptor tyrosine kinase.

diffusing into cells and stimulating the cyclase directly.

A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to ________________. Question options: a) disassemble its nuclear lamina at prometaphase. b) begin to assemble a mitotic spindle. c) reassemble its nuclear envelope at telophase. d) condense its chromosomes at prophase.

disassemble its nuclear lamina at prometaphase.

Cells in the G0 state ________________. Question options: a) do not divide. b) have entered this arrest state from either G1 or G2. c) cannot re-enter the cell cycle. d) have duplicated their DNA.

do not divide.

Figure Q12-56 illustrates changes in membrane potential during the formation of an action potential. What membrane characteristic or measurement used to study action potentials is indicated by the arrow?Figure Q12-56 Question options: a) action potential b) threshold potential c) effect of a depolarizing stimulus d) resting membrane potential

effect of a depolarizing stimulus

Signal sequences that direct proteins to the correct compartment are _________. Question options: a) always removed once a protein is at the correct destination. b) added to a protein by a protein translocator. c) encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination. d) added to proteins through post-translational modification.

encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination.

Signal sequences that direct proteins to the correct compartment are _________. Question options: a) always removed once a protein is at the correct destination. b) added to proteins through post-translational modification. c) added to a protein by a protein translocator. d) encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination.

encoded in the amino acid sequence and sufficient for targeting a protein to its correct destination.

A receptor tyrosine kinase (RTK) is a(n) _______________ receptor. Question options: a) ion-channel-coupled b) enzyme-coupled c) G protein-coupled d) none of these

enzyme-coupled

Below is a list of molecules with different chemical characteristics. Knowing that all molecules will eventually diffuse across a phospholipid bilayer, select the option below that most accurately predicts the relative rates of diffusion of these molecules (fastest to slowest).alanineestrogenpropanolsodium Question options: a) sodium > propanol > alanine > estrogen b) estrogen > propanol > alanine > sodium c) estrogen > propanol > sodium > alanine d) alanine > propanol > sodium > estrogen

estrogen > propanol > alanine > sodium

Proteins in the plasma membrane that are participating in cell to cell interactions are usually Question options: free to move laterally within the membrane. alpha helices. restricted to a certain area in the plasma membrane. also providing additional mechanical strength to the membrane.

free to move laterally within the membrane

Membranes are said to be "fluid" because the individual molecules that are present are Question options: always fixed in place. able to transfer from one cell to another. generally free to move laterally and rotate.

generally free to move laterally and rotate.

Which of the following does not occur during M phase in animal cells? Question options: a) growth of the cell b) attachment of chromosomes to microtubules c) breakdown of nuclear envelope d) condensation of chromosomes

growth of the cell

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________. Question options: a) scaffold. b) hormone. c) neurotransmitter. d) dissolved gas.

hormone

Trans-membrane domains can be predicted with analysis such as a(n) Question options: western blot isoelectric focusing hydropathy plot SDS-PAGE gel

hydropathy plot

Phospholipids assemble spontaneously into bilayers driven by the attraction of their "tail" portions to each other and of their "head" portions to an aqueous solvent. The tail regions are: Question options: a) hydrophilic. b) molecularly charged. c) adhesive. d) hydrophobic. e) cohesive.

hydrophobic.

Transmembrane proteins that make up enzymes in the plasma membrane are made up of hydrophilic and hydrophobic regions. Most amino acids embedded in the membrane are ________, while most amino acids facing the extracellular fluid are __________. Question options hydrophilic;hydrophilic hydrophilic;hydrophobic hydrophobic;hydrophobic hydrophobic;hydrophilic lipophilic; lipophobic

hydrophobic;hydrophilic

A mutant yeast strain stops proliferating when shifted from 25°C to 37°C. When these cells are analyzed at the two different temperatures, using a machine that sorts cells according to the amount of DNA they contain, the graphs in Figure Q18-3 are obtained.Figure 18-3Which of the following would not explain the results with the mutant? Question options: a) inability to initiate DNA replication b) inability to activate proteins needed to enter S phase c) inability to begin M phase d) inappropriate production of a signal that causes the cells to remain in G1

inability to begin M phase

The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by ______. Question options: a) inhibiting cyclin transcription. b) phosphorylating Cdk. c) activating apoptosis. d) marking cyclins for destruction by proteolysis.

inhibiting cyclin transcription.

A protein kinase can act as an integrating device in signaling if it ___________________. Question options: a) phosphorylates more than one substrate. b) catalyzes its own phosphorylation. c) initiates a phosphorylation cascade involving two or more protein kinases. d) is activated by two or more proteins in different signaling pathways.

initiates a phosphorylation cascade involving two or more protein kinases.

A protein that passes through the membranes is Question options: peripheral integral hydrophilic denatured

integral

Cells that are terminally differentiated ______________________. Question options: a) can no longer undergo cell division. b) are unable to move. c) will undergo apoptosis within a few days. d) no longer produce RNAs.

can no longer undergo cell division.

Apoptosis differs from necrosis in that necrosis ________________. Question options: a) involves a caspase cascade. b) requires the reception of an extracellular signal. c) causes DNA to fragment. d) causes cells to swell and burst, whereas apoptotic cells shrink and condense.

causes cells to swell and burst, whereas apoptotic cells shrink and condense.

The principal microtubule-organizing center in animal cells is the ____________. Question options: a) cell cortex. b) centrosome. c) kinetochore. d) centromere.

centrosome.

Vesicles from the ER enter the Golgi at the ______. Question options: a) trans Golgi network. b) cis Golgi network. c) medial cisternae. d) trans cisternae.

cis Golgi network.

At the end of DNA replication, the sister chromatids are held together by the ___________. Question options: a) cohesins. b) histones. c) kinetochores. d) securins.

cohesins.

At the end of DNA replication, the sister chromatids are held together by the ___________. Question options: a) securins. b) histones. c) kinetochores. d) cohesins.

cohesins.

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to _________. Question options: a) activate the RTK. b) directly phosphorylate Akt. c) create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane. d) to create DAG.

create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane.

Levels of Cdk activity change during the cell cycle, in part because ________________. Question options: a) cyclin levels change during the cycle. b) the Cdks activate the cyclins. c) Cdk degradation precedes entry into the next phase of the cell cycle. d) the Cdks phosphorylate each other.

cyclin levels change during the cycle.

The G1 DNA damage checkpoint ________________. Question options: a) involves the inhibition of cyclin-Cdk complexes by p21. b) involves the degradation of p53. c) is activated by errors caused during DNA replication. d) causes cells to proceed through S phase more quickly.

involves the inhibition of cyclin-Cdk complexes by p21.

Which of the following statements is true? Question options: a) Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism. b) The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells. c) Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal. d) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling.

d) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling.

A malignant tumor is more dangerous than a benign tumor because ______________________. Question options: a) its cells attack and phagocytose neighboring normal tissue cells. b) its cells are proliferating faster. c) it causes neighboring cells to mutate. d) its cells invade other tissues.

its cells invade other tissues.

The principal components of cell membranes are Question options: a) carbohydrates. b) nucleic acids. c) proteins. d) glycoproteins. e) lipids.

lipids.

Which word or phrase below best describes the phase in mitosis depicted in Figure Q18-41? Question options: a) metaphase b) anaphase c) prometaphase d) S-phase checkpoint

metaphase

Disassembly of the nuclear envelope ________________. Question options: a) causes the inner nuclear membrane to separate from the outer nuclear membrane. b) results in the conversion of the nuclear envelope into protein-free membrane vesicles. c) is triggered by the phosphorylation of integrins. d) must occur for kinetochore microtubules to form in animal cells.

must occur for kinetochore microtubules to form in animal cells.

Which of the following statements is correct? Kinesins and dyneins ____________________. Question options: a) have tails that bind to the filaments. b) often move in opposite directions to each other. c) move along both microtubules and actin filaments. d) derive their energy from GTP hydrolysis.

often move in opposite directions to each other.

Which cellular structure makes it possible for a cell to differ structurally and biochemically from its surroundings? Question options: a) nucleus b) nucleolus c) plasma membrane d) endoplasmic reticulum e) cell wall

plasma membrane

When a terminally differentiated cell in an adult body dies, it can typically be replaced in the body by a stock of ________. Question options: a) embryonic stem cells b) Wnt proteins. c) cells more apically located than the terminally differentiated cells. d) proliferating precursor cells.

proliferating precursor cells.

Cytokinesis in animal cells ________________. Question options: a) is assisted by motor proteins that pull on microtubules attached to the cell cortex. b) is often followed by phosphorylation of integrins in the plasma membrane. c) leaves a small circular "scar" of actin filaments on the inner surface of the plasma membrane. d) requires ATP.

requires ATP.

Figure Q12-54 illustrates changes in membrane potential during the formation of an action potential. What membrane characteristic or measurement used to study action potentials is indicated by the arrow?Figure Q12-54 Question options: a) threshold potential b) resting membrane potential c) effect of a depolarizing stimulus d) action potential

resting membrane potential

Which of the following structures shorten during muscle contraction? Question options: a) sarcomeres b) actin filaments c) flagella d) myosin filaments

sarcomeres

Which of the following items is not important for flagellar movement? Question options: a) sarcoplasmic reticulum b) dynein c) ATP d) microtubules

sarcoplasmic reticulum

Which steps in muscle contraction require ATP? Question options: transport of calcium ions back into the sarcoplasmic reticulum to allow relaxation all of these none of these the sodium-potassium pump to generate resting membrane potential sliding filament mechanism of muscle contraction

sliding filament mechanism of muscle contraction

Transporters, in contrast to channels, work by ________________. Question options: a) filtering solutes by charge. b) specific binding to solutes. c) a gating mechanism. d) filtering solutes by size.

specific binding to solutes.

The length of time a G protein will signal is determined by _______. Question options: a) the activity of phosphatases that turn GTP into GDP. b) the GTPase activity of Gα c) the degradation of the G protein after Gα separates from Gβγ d) the activity of phosphatases that turn off G proteins by dephosphorylating Gα.

the activity of phosphatases that turn off G proteins by dephosphorylating Gα.

Progression through the cell cycle requires a cyclin to bind to a Cdk because _________. Question options: a) cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle. b) without cyclin binding, a cell-cycle checkpoint will be activated. c) the binding of a cyclin to Cdk is required for Cdk enzymatic activity. d) the cyclins are the molecules with the enzymatic activity in the complex.

the binding of a cyclin to Cdk is required for Cdk enzymatic activity.

Proteins that are fully translated in the cytosol and lack a sorting signal will end up in ____. Question options: a) the nuclear membrane. b) the cytosol. c) the mitochondria. d) the interior of the nucleus.

the cytosol.

Proteins that are fully translated in the cytosol and lack a sorting signal will end up in ____. Question options: a) the nuclear membrane. b) the interior of the nucleus. c) the cytosol. d) the mitochondria.

the cytosol.

Figure Q12-53 illustrates changes in membrane potential during the formation of an action potential. What membrane characteristic or measurement used to study action potentials is indicated by the arrow?Figure Q12-53 Question options: a) threshold potential b) action potential c) effect of a depolarizing stimulus d) resting membrane potential

threshold potential

Active transport, the moving of molecules from areas of low concentration to those of high concentration across the membrane, is usually coupled to processes that: Question options: a) gain energy for the cell. b) counteract osmotic stress. c) amplify cellular response to signal molecules. d) establish a dynamic equilibrium with no net gain or loss in energy for the cell. e) use energy.

use energy.

Which of the following is required for the secretion of neurotransmitters in response to an action potential? Question options: a) neurotransmitter receptors b) voltage-gated Ca2+ channels c) voltage-gated K+ channels d) Na+-K+ pumps

voltage-gated Ca2+ channels

An individual transport vesicle ________. Question options: a) is endocytic if it is traveling toward the plasma membrane. b) will fuse with only one type of membrane. c) is enclosed by a membrane with the same lipid and protein composition as the membrane of the donor organelle. d) contains only one type of protein in its lumen.

will fuse with only one type of membrane.

The graph in Figure Q17-31 shows the time course of the polymerization of pure tubulin in vitro. Assume that the starting concentration of free tubulin is higher than it is in cells.Figure Q17-31Three parts of the curve are labeled above it as A, B, and C. You conduct a similar in vitro tubulin-polymerization experiment, only you include purified centrosomes in your preparation. When you plot your data, which part of your graph should be most dissimilar to the curve shown in Figure Q17-31? Question options: a) B b) None. The shape of my graph should be identical to the graph produced when tubulin is polymerized in the absence of purified centrosomes. c) A d) C

A

Which of the following statements about the anaphase-promoting complex (APC) is false? Question options: a) It promotes the degradation of proteins that regulate M phase. b) It is continuously active throughout the cell cycle. c) M-Cdk stimulates its activity. d) It inhibits M-Cdk activity.

It is continuously active throughout the cell cycle.

Which of the following statements about apoptosis is true? Question options: a) Cells that constitutively express Bcl2 will be more prone to undergo apoptosis. b) The prodomain of procaspases contains the catalytic activity necessary for procaspase activation. c) Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria. d) Bax and Bak promote apoptosis by binding to procaspases in the apoptosome.

Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria.

Figure Q17-40A shows how the movement of dynein causes the flagellum to bend. If instead of the normal situation, the polarity of the adjacent doublet of microtubules were to be reversed (see Figure Q17-40B), what do you predict would happen?Figure Q17-40 Question options: a) Bending would occur exactly as diagrammed in Figure Q17-40A. b) No bending would occur. c) The two microtubule doublets would slide away from each other. d) Bending would occur, except that the right microtubule doublet would move down relative to the left one.

Bending would occur, except that the right microtubule doublet would move down relative to the left one.

Which of the following best describes the behavior of a gated channel? Question options: a) It opens more widely as the stimulus becomes stronger. b) It stays closed when stimulated. c) It opens more frequently in response to a given stimulus. d) It remains closed if unstimulated.

It opens more frequently in response to a given stimulus.

Which of the following compounds is amphipathic? Question options: A) H2O B) CH3CH2CH2CH2CH3 C) HOOCCOOH D) CH3CH2CH2CH2COOH E) Both A and D are correct

CH3CH2CH2CH2COOH

You are examining a cell line in which activation of the Rho family member Rac promotes lamellipodia formation. Rac is a GTPase involved in signaling. Which of the following statements is most likely to be true? Question options: a) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more branched actin filaments than normal cells. b) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more unbranched actin filaments than normal cells. c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more unbranched actin filaments than normal cells. d) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells

Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells

Which of the following statements about tumor suppressor genes is false? Question options: a) Inactivation of tumor suppressor genes leads to enhanced cell survival and proliferation. b) Gene amplification of a tumor suppressor gene is less dangerous than gene amplification of a proto-oncogene. c) Individuals with only one functional copy of a tumor suppressor gene are more prone to cancer than individuals with two functional copies of a tumor suppressor gene. d) Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells.

Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells.

Which of the following choices reflects the appropriate order of locations through which a protein destined for the plasma membrane travels? Question options: a) lysosome endosome plasma membrane b) ER Golgi plasma membrane c) ER lysosome plasma membrane d) Golgi lysosome plasma membrane

ER Golgi plasma membrane

Negatively charged ions are required to balance the net positive charge from metal ions such as K+, Na+, and Ca2+. Which of the following negatively charged ions is the most abundant outside the cell and which ion does most often neutralize (written in parentheses)? Question options: a) PO43- (K+) b) Cl- (Ca2+) c) Cl- (Na+) d) PO43- (Ca2+)

Cl- (Na+)

Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure. Figure Q17-10 shows the structure of an intermediate filament subunit. You are interested in how intermediate filaments are formed, and you create an intermediate filament subunit whose a-helical region is twice as long as that of a normal intermediate filament by duplicating the normal a-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFad. If you were to assemble intermediate filaments using IFad as the subunit, which of the following predictions describes the most likely outcome?Figure Q17-10 Question options: a) Filaments assembled using IF ad will form dimers that are twice as long as dimers assembled from normal intermediate filaments. b) Dimers of IF ad will form by interactions with the N-terminal globular head and the C-terminal globular tail. c) Sixteen tetramers assembled from IF ad will be needed for a ropelike structure to form. d) Filaments assembled using IF ad will interact with different cytoskeletal components.

Filaments assembled using IF ad will form dimers that are twice as long as dimers assembled from normal intermediate filaments.

Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is false? Question options: a) Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways. b) Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family. c) Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal. d) Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract.

Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family.

Which of the following statements is true? Question options: a) Anaphase A must be completed before anaphase B can take place. b) In cells in which anaphase B predominates, the spindle will elongate much less than in cells in which anaphase A dominates. c) In anaphase A, both kinetochore and interpolar microtubules shorten. d) In anaphase B, microtubules associated with the cell cortex shorten.

In anaphase B, microtubules associated with the cell cortex shorten.

If Na+ channels are opened in a cell that was previously at rest, how will the resting membrane potential be affected? Question options: a) It is permanently reset. b) It becomes more negative. c) The membrane potential is not affected by Na+. d) It becomes more positive.

It becomes more positive.

What is the role of the nuclear localization sequence in a nuclear protein? Question options: a) It is a hydrophobic sequence that enables the protein to enter the nuclear membranes. b) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore. c) It prevents the protein from diffusing out of the nucleus through nuclear pores. d) It aids in protein unfolding so that the protein can thread through nuclear pores.

It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore.

What is the role of the nuclear localization sequence in a nuclear protein? Question options: a) It prevents the protein from diffusing out of the nucleus through nuclear pores. b) It is a hydrophobic sequence that enables the protein to enter the nuclear membranes. c) It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore. d) It aids in protein unfolding so that the protein can thread through nuclear pores.

It is bound by cytoplasmic proteins that direct the nuclear protein to the nuclear pore.

The lab you work in has discovered a previously unidentified extracellular signal molecule called QGF, a 75,000-dalton protein. You add purified QGF to different types of cells to determine its effect on these cells. When you add QGF to heart muscle cells, you observe an increase in cell contraction. When you add it to fibroblasts, they undergo cell division. When you add it to nerve cells, they die. When you add it to glial cells, you do not see any effect on cell division or survival. Given these observations, which of the following statements is most likely to be true? Question options: a) Because it acts on so many diverse cell types, QGF probably diffuses across the plasma membrane into the cytoplasm of these cells. b) Heart muscle cells, fibroblasts, and nerve cells must all have the same receptor for QGF. c) QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed. d) Glial cells do not have a receptor for QGF.

QGF activates different intracellular signaling pathways in heart muscle cells, fibroblasts, and nerve cells to produce the different responses observed.

_____ are membrane proteins that bind to signals by which cells communicate. Question options: Receptors Enzymes Carriers Cell-identity markers Cell-adhesion molecules

Receptors

In a method called patch-clamping, a glass capillary can be converted into a microelectrode that measures the electrical currents across biological membranes. Which of the following is not true about the patch-clamp method? Question options: a) The aperture in the glass capillary used to make a microelectrode is about 1 μm in diameter. b) Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli. c) If the experimental conditions are held constant, fluctuations in electrical currents across the patch of membrane are still observed. d) The glass capillary adheres to a "patch" of membrane through the application of suction.

Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli.

Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold? Question options: a) Some channels remain closed and some open completely. b) All channels open partly, each to a different degree. c) All channels open completely. d) All channels open partly, to the same degree.

Some channels remain closed and some open completely.

Figure Q15-34 shows the organization of a protein that normally resides in the plasma membrane. Box 1 represents the N-terminal signal sequence. Box 2 represents a stop-transfer sequence. Given this diagram, which of the following statements must be true? Figure Q15-34 Question options: a) The N-terminus of this protein is cytoplasmic. b) The C-terminus of this protein is cytoplasmic. c) The mature version of this protein will span the membrane twice, with both the N- and C-terminus in the cytoplasm. d) None of the above.

The C-terminus of this protein is cytoplasmic.

Which of the following statements about vesicular membrane fusion is false? Question options: a) The hydrophilic surfaces of membranes have water molecules associated with them that must be displaced before vesicle fusion can occur. b) The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion. c) The interactions of the v-SNAREs and the t-SNAREs pull the vesicle membrane and the target organelle membrane together so that their lipids can intermix. d) Membrane fusion does not always immediately follow vesicle docking.

The GTP hydrolysis of the Rab proteins provides the energy for membrane fusion.

Microtubules are important for transporting cargo in nerve cell axons, as diagrammed in Figure Q17-33. Notice that the two types of cargo are traveling in opposite directions. Which of the following statements is likely to be false?Figure Q17-33 Question options: a) The gray cargo is attached to dynein. b) The black cargo and the gray cargo are moving along microtubules of opposite polarity. c) The black cargo moving toward the axon terminal contains a domain that specifically interacts with the tail domain of a particular kind of motor. d) The black cargo and the gray cargo require ATP hydrolysis for their motion.

The black cargo and the gray cargo are moving along microtubules of opposite polarity.

K+ leak channels are found in the plasma membrane. These channels open and close in an unregulated, random fashion. What do they accomplish in a resting cell? Question options: a) They set the K+ concentration gradient to zero. b) They set the membrane potential to zero. c) They disrupt the resting membrane potential. d) They keep the electrochemical gradient for K+ at zero.

They keep the electrochemical gradient for K+ at zero.

Figure Q15-57 shows the orientation of the Krt1 protein on the membrane of a Golgi-derived vesicle that will fuse with the plasma membrane.Figure Q15-57Given this diagram, which of the following statements is true? Question options: a) When this vesicle fuses with the plasma membrane, the C-terminus of Krt1 will be inserted into the plasma membrane. b) When this vesicle fuses with the plasma membrane, the entire Krt1 protein will be secreted into the extracellular space. c) When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be cytoplasmic. d) When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be in the extracellular space.

When this vesicle fuses with the plasma membrane, the N-terminus of Krt1 will be in the extracellular space.

Male cockroaches with mutations that strongly decrease the function of an RTK called RTKX are oblivious to the charms of their female comrades. This particular RTK binds to a small molecule secreted by sexually mature females. Most males carrying loss-of-function mutations in the gene for Ras protein are also unable to respond to females. You have just read a paper in which the authors describe how they have screened cockroaches that are mutant in RTKX for additional mutations that partly restore the ability of males to respond to females. These mutations decrease the function of a protein that the authors call Z. Which of the following types of protein could Z be? Explain your answer. Question options: a) a transcriptional regulator required for the expression of the Ras gene b) a protein that stimulates hydrolysis of GTP by the Ras protein c) an adaptor protein that mediates the binding of the RTKX to the Ras protein d) a protein that activates the Ras protein by causing Ras to exchange GDP for GTP

a protein that stimulates hydrolysis of GTP by the Ras protein

Ras is a GTP-binding protein that is often defective in cancer cells. A common mutation found in cancer cells causes Ras to behave as though it were bound to GTP all the time, which will cause cells to divide inappropriately. From this description, the normal Ras gene is _______. Question options: a) a proto-oncogene. b) a gain-of-function mutation. c) a tumor suppressor. d) an oncogene.

a proto-oncogene.

Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2? Question options: a) The cell would enter M phase under conditions when normal cells would not. b) The cell would pass through M phase more slowly than normal cells c) The cell would be unable to enter G2. d) The cell would be unable to enter M phase.

a) The cell would enter M phase under conditions when normal cells would not.

Which of the following statements about the structure of microtubules isfalse? Question options: a) Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity. b) a-Tubulin and b-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments. c) Microtubules are built from protofilaments that come together to make a hollow structure. d) The two ends of a protofilament are chemically distinct, with a-tubulin exposed at one end and b-tubulin exposed at the other end.

a-Tubulin and b-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.

Which of the following statements is true? Question options: a) A cell-surface receptor capable of binding only one type of signal molecule can mediate only one kind of cell response. b) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior. c) Any foreign substance that binds to a receptor for a normal signal molecule will always induce the same response that is produced by that signal molecule on the same cell type. d) To function, all extracellular signal molecules must be transported by their receptor across the plasma membrane into the cytosol.

b) Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior.

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. Question options: a) neuronal b) contact-dependent c) endocrine d) paracrine

b) contact-dependent

The concentration of mitotic cyclin (M cyclin) ________________. Question options: a) rises markedly during M phase. b) is highest in G1 phase. c) falls toward the end of M phase as a result of ubiquitylation and degradation. d) is activated by phosphorylation.

c) falls toward the end of M phase as a result of ubiquitylation and degradation.

All members of the steroid hormone receptor family __________________. Question options: a) do not undergo conformational changes. b) are cell-surface receptors. c) interact with signal molecules that diffuse through the plasma membrane. d) are found only in the cytoplasm.

c) interact with signal molecules that diffuse through the plasma membrane.