Deck 11: Cell Communication

Question 1

Which of the following is true of transcription factors?

A)They regulate the synthesis of DNA in response to a signal.
B)They transcribe ATP into cAMP.
C)They initiate the epinephrine response in animal cells.
D)They control gene expression.
E)They regulate the synthesis of lipids in the cytoplasm.

Answer 1

D

Question 2

In yeast signal transduction,the yeast cells

A)must physically and directly interact.
B)produce signal molecules that change themselves so they can interact with one another.
C)produce response molecules that diffuse to other yeast cells.
D)secrete molecules that result in response by other yeast cells.
E)mate, after which the new cells secrete hybrid signals.

Answer 2

D

Question 3

Which of the following is usually true for receptors?

A)They lead to changes in intracellular ion concentration.
B)They open and close in response to protein signals.
C)They are only attached to one membrane surface: exterior or interior.
D)They preferentially bind with lipid signal molecules.
E)They change their conformation after binding with signal molecules.

Answer 3

E

Question 4

Which of the following dictates the use of Herceptin in breast cancer treatment?

A)If Herceptin is found in the breast lymph nodes of the patient.
B)If HER2, administered by injection, is in sufficient concentration.
C)If the patient's cancer cells have excessive levels of HER2.
D)If the patient's genome codes for the HER2 receptor.
E)If the patient's genome codes for the manufacture of Herceptin.

Question 5

What does yeast cell mating factor do?

A)acts 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
E)allows two cells with the same mating factor (e.g. a)to mate

Question 6

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

A)formation of mating complexes
B)secretion of apoptotic signals
C)aggregation of bacteria
D)secretion of substances that inhibit foreign bacteria
E)digestion of unwanted parasite populations

Question 7

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

A)brings a conformational change to each protein.
B)requires binding of a hormone to a cytosol receptor.
C)cannot occur in yeasts because they lack protein phosphatases.
D)requires phosphorylase activity.
E)allows target cells to change their shape and therefore their activity.

Question 8

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

A)Plant hormones interact primarily with intracellular receptors.
B)Plant hormones may travel in air or through vascular systems.
C)Animal hormones are found in much greater concentration.
D)Plant hormones are synthesized from two or more distinct molecules.
E)Animal hormones are primarily for mating and embryonic development.

Question 9

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

A)receptor
B)relay molecule
C)transducer
D)signal molecule
E)endocrine molecule

Question 10

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

A)the active site of an allosteric enzyme that binds to a specific substrate.
B)tRNA specifying which amino acids are in a polypeptide.
C)a metabolic pathway operating within a specific organelle.
D)an enzyme having an optimum pH and temperature for activity.
E)an antibody in the immune system.

Question 11

The receptors for a group of signalling molecules known as growth factors are often

A)ligand-gated ion channels.
B)G protein-coupled receptors.
C)cyclic AMP.
D)receptor tyrosine kinases.
E)neurotransmitters.

Question 12

How does aldosterone function?

A)acts as a signal receptor that activates tyrosine kinases.
B)binds with a receptor protein that enters the nucleus and activates specific genes.
C)acts as a steroid signal receptor that activates ion channel proteins.
D)becomes a second messenger that inhibits adenylyl cyclase.
E)coordinates a phosphorylation cascade that increases spermatogenesis.

Question 13

Which type of receptor in the plasma membrane reacts by forming dimers,adding phosphate groups,and then activating relay proteins?

A)G protein-coupled receptors
B)ligand-gated ion channels
C)steroid receptors
D)quorum sensing receptors

Question 14

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

A)hormonal signalling
B)autocrine signalling
C)paracrine signalling
D)endocrine signalling
E)synaptic signalling

Question 15

Which of the following is true of steroid receptor interactions?

A)The receptor molecules are themselves lipids.
B)The steroid can cross the plasma membrane.
C)The unbound steroid receptors are quickly recycled by lysosomes.
D)The concentration of steroid receptors must be relatively high in most cells.
E)The receptor molecules are free to move in and out of most organelles.

Question 16

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

A)It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.
B)It could activate only the epinephrine system.
C)It would be able to carry out reception and transduction but would not be able to respond to a signal.
D)It would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.
E)It would employ a transduction pathway directly from an external messenger.

Question 17

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

A)blockage of the synaptic signal
B)loss of transcription factors
C)insufficient ATP levels in the cytoplasm
D)low oxygen concentration around the cell
E)low levels of protein kinase in the cell

Question 18

Epinephrine signals which of the following?

A)a decrease in levels of cAMP as a result of bypassing the plasma membrane
B)lower blood glucose by binding to liver cells
C)interactions with insulin inside muscle cells
D)interactions directly with glycogen phosphorylase
E)elevation of cytosolic concentrations of cyclic AMP

Question 19

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

A)They might compensate by receiving nutrients via a factor.
B)They could develop normally in response to neurotransmitters instead.
C)They could divide but never reach full size.
D)They might not be able to grow and multiply in response to growth factors from nearby cells.
E)Cells do not need local regulators.

Question 20

When yeast cells release mating factors,what happens?

A)The mating factors induce changes in the cells that lead to cell fusion.
B)The affected cells produce more of the a factor as a positive feedback.
C)One cell nucleus binds the mating factors and produces a new nucleus in the opposite cell.
D)The mating factors stimulate cell membrane disintegration, releasing the mating factors and leading to new yeast cells.
E)The cells in turn release a growth factor that stimulates mitosis in both cells.

Question 21

The toxin of Vibrio cholerae causes profuse diarrhea because it

A)modifies a G protein involved in regulating salt and water secretion.
B)decreases the cytosolic concentration of calcium ions, making the cells hypotonic.
C)binds with adenylyl cyclase and triggers the formation of cAMP.
D)signals IP₃ to act as a second messenger for the release of calcium.
E)modifies calmodulin and activates a cascade of protein kinases.

Question 22

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

A)Most of the steps were already in place because they are steps in other pathways.
B)Multiple steps in a pathway require the least amount of ATP.
C)Multiple steps provide for greater possible amplification of a signal.
D)Each individual step can remove excess phosphate groups from the cytoplasm.
E)Each step can be activated by several G proteins simultaneously.

Question 23

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

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

Question 24

A drug designed to inhibit the response of cells to a growth factor would almost certainly result in which of the following?

A)lower cytoplasmic levels of cAMP
B)an increase in receptor tyrosine kinase activity
C)a decrease in transcriptional activity of certain genes
D)an increase in cytosolic calcium concentration
E)a decrease in G protein activity

Question 25

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

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

Question 26

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)phosphorylase activity and the catabolism of glucose
E)adenylyl cyclase activity and the conversion of cAMP to AMP

Question 27

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

A)block the response of epinephrine
B)decrease the amount of cAMP in the cytoplasm
C)block the activation of G proteins in response to epinephrine binding to its receptor
D)prolong the effect of epinephrine by maintaining elevated cAMP levels in the cytoplasm
E)block the activation of protein kinase A

Question 28

What explains the increased concentration of Ca²⁺ in the ER?

A)Calcium ions are actively imported from the cytoplasm into the ER.
B)Calcium concentration is kept low in the cytoplasm because of its high usage level.
C)Calcium cannot enter the plasma membrane through ion channels.
D)Calcium levels in the blood or other body fluids are extremely low.
E)The Ca ions are recycled from other molecules in the ER.

Question 29

What are scaffolding proteins?

A)ladderlike proteins that allow receptor-ligand complexes to climb through cells from one position to another
B)microtubular protein arrays that allow lipid-soluble hormones to get from the cell membrane to the nuclear pores
C)large molecules to which several relay proteins attach to facilitate cascade effects
D)relay proteins that orient receptors and their ligands in appropriate directions to facilitate their complexing
E)proteins that can reach into the nucleus of a cell to affect transcription

Question 30

The best description of the function of phosphatases in signal transduction is that it

A)moves the phosphate group of the transduction pathway to the next molecule of a series.
B)prevents a protein kinase from being reused when there is another extracellular signal.
C)amplifies the transduction signal so it affects multiple transducers.
D)amplifies the second messengers such as cAMP.
E)inactivates protein kinases and turns off the signal transduction.

Question 31

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

A)increases the available concentration of phosphate.
B)decreases the amount of G protein in the membrane.
C)hydrolyzes GTP binding to G protein.
D)converts cGMP to GTP.
E)phosphorylates protein kinases.

Question 32

The termination phase of cell signalling requires which of the following?

A)removal of the receptor
B)activation of a different set of relay molecules
C)converting ATP to cAMP
D)reduction of signal and reversion of receptor to inactive state
E)apoptosis

Question 33

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 and then enter the cell and eventually the nucleus.
D)Toxins such as those that cause botulism and cholera interfere with the ability of activated G proteins to hydrolyze GTP to GDP, resulting in phosphodiesterase activity in the absence of an appropriate signal molecule.
E)Protein kinase A activation is one possible result of signal molecules binding to G protein-coupled receptors.

Question 34

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

A)removal of serine/threonine phosphate acceptors from transduction pathways in colon pre-cancerous growths
B)alteration of protein kinases in cell cycle regulation in order to slow cancer growth
C)increase in calcium ion uptake into the cytoplasm in order to modulate the effects of environmental carcinogens
D)expansion of the role of transduction inhibitors in the cells before they give rise to cancer
E)increase in the concentration of phosphodiesterases in order to produce more AMP

Question 35

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

A)Estrogen is produced in very large concentration and therefore diffuses widely.
B)Estrogen has specific receptors inside several cell types, but each cell responds in the same way to its binding.
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 of which have different responses to its binding.
E)The subcomponents of estrogen, when metabolized, can influence cell response.

Question 36

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

A)G protein-coupled receptor signalling
B)ligand-gated ion channel signalling
C)adenylyl cyclase activity
D)phosphatase activity
E)receptor tyrosine kinase activity

Question 37

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

A)protein kinase activity
B)adenylyl cyclase activity
C)GTPase activity
D)protein phosphatase activity
E)phosphorylase activity

Question 38

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
E)Any of the 20 amino acids are equally phosphorylated.

Question 39

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

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

Question 40

Which of the following is the original signal inhibited by Viagra?

A)hydrolysis of cGMP to GMP.
B)hydrolysis of GTP to GDP.
C)phosphorylation of GDP.
D)dephosphorylation cGMP.
E)removal of GMP from the cell.

Question 41

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

A)Growth factor ligands do not bind as efficiently to receptors.
B)Their lower hormone concentrations elicit a lesser response.
C)cAMP levels change very frequently.
D)Enzymatic activity declines.
E)ATP production decreases.

Question 42

Use the following figure to answer the questions below.

Which of the following types of signalling is represented in the figure?

A)autocrine
B)paracrine
C)hormonal
D)synaptic
E)long-distance

Question 43

Coordinated,systematic cell death is known as

A)senescence.
B)cancer.
C)apoptosis.
D)trophic cascade.
E)synaptic signalling.

Question 44

Select the appropriate description of apoptosis.

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.
E)Apoptosis only occurs in old cells.

Question 45

Apoptosis protects healthy "neighbours" from a dying cell by preventing

A)cell death spreading from one cell to the next via paracrine signals.
B)lysosomal enzymes exiting the dying cell that would damage surrounding cells.
C)release of cellular energy that would interfere with the neighbours' energy budget.
D)bits of membrane from the dying cell merging with neighbours and bringing in foreign receptors.
E)neighbouring cells activating immunological responses.

Question 46

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

A)neurodegeneration
B)activation of a developmental pathway found in the worm but not in humans
C)a form of cancer in which there is insufficient apoptosis
D)webbing of fingers or toes
E)excess skin exfoliation

Question 47

Sutherland's research showed that cell-to-cell communication can be divided into three distinct parts that follow a particular sequence.In order from first to last,these are

A)transduction, response, reception.
B)reception, transduction, response.
C)transcription, translation, response.
D)transduction, transcription, translation.
E)first messenger, second messenger, product.

Question 48

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

A)The animal has as many genes as complex organisms, but finding those responsible is easier than in a more complex organism.
B)The nematode undergoes a fixed and easy-to-visualize number of apoptotic events during its normal development.
C)This plant has a long-studied aging mechanism that has made understanding its death just a last stage.
D)While the organism ages, its cells die progressively until the whole organism is dead.
E)All of its genes are constantly being expressed so all of its proteins are available from each cell.

Question 49

Which of the following is characterized by hydrophobic molecules passing through the plasma membrane and interacting with cytosolic receptors?

A)hormonal signalling
B)autocrine signalling
C)paracrine signalling
D)endocrine signalling
E)synaptic signalling

Question 50

Use the following figure to answer the questions below.

In the above diagram,the structure labelled C is a(n)

A)second messenger.
B)activated relay molecule.
C)ligand.
D)receptor.
E)phosphorylation cascade.

Question 51

Protein phosphorylation is commonly involved with all of the following except

A)regulation of transcription by extracellular signalling molecules.
B)enzyme activation.
C)activation of G protein-coupled receptors.
D)activation of receptor tyrosine kinases.
E)activation of protein kinase molecules.

Question 52

Use the following figure to answer the questions below.

In the above diagram,the structure labelled B is a(n)

A)transcription factor.
B)activated relay molecule.
C)ligand.
D)plasma membrane receptor.
E)intracellular receptor.

Question 53

Which of the following describes the events of apoptosis?

A)The cell dies, it is lysed, its organelles are phagocytized, and its contents are recycled.
B)Its DNA and organelles become fragmented, it dies, and it is phagocytized.
C)The cell dies and the presence of its fragmented contents stimulates nearby cells to divide.
D)Its DNA and organelles are fragmented, the cell shrinks and forms blebs, and the cell self-digests.
E)Its nucleus and organelles are lysed, then the cell enlarges and bursts.

Question 54

Use the following figure to answer the questions below.

In the above diagram,the structure labelled D is a(n)

A)second messenger.
B)activated relay molecule.
C)ligand.
D)receptor.
E)phosphorylation cascade.

Question 55

Use the following figure to answer the questions below.

In the above diagram,the structure labelled A is a(n)

A)second messenger.
B)activated relay molecule.
C)ligand.
D)receptor.
E)phosphorylation cascade.

Question 56

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

A)It prevents the caspase activity of ced-3 and ced-4.
B)Ced-9 remains inactive until it is signalled by ced-3 and other caspases.
C)Ced-9 cleaves to produce ced-3 and ced-4.
D)Ced-9 enters the nucleus and activates apoptotic genes.
E)Ced-9 prevents blebbing by its action on the cell membrane.

Question 57

A molecule that specifically binds to another molecule (often a larger one)is known as a(n)

A)ligand.
B)receptor.
C)transcription factor.
D)activator.
E)scaffolding protein.

Question 58

Which of the following is characterized by molecules from an adjacent cell being released to interact with neighbouring cells by binding with surface receptors and opening ion channels?

A)hormonal signalling
B)autocrine signalling
C)paracrine signalling
D)endocrine signalling
E)synaptic signalling

Question 59

Where do apoptotic signals come from?

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

Question 60

Use the following figure to answer the questions below.

In the figure,the dots in the space between the two structures represent which of the following?

A)receptor molecules
B)signal transducers
C)neurotransmitters
D)hormones
E)pheromones

Question 61

What must a target organ do to respond to a particular hormone?

A)modify its plasma membrane to assist transport of the hormone entering the cytoplasm
B)be from the same cell type as the organ that produced the hormone
C)experience an imbalance that disrupts its normal function
D)have receptors that recognize and bind the hormone molecule
E)break down the hormone

Question 62

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.
E)channel protein shape change.

Question 63

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
E)5, 1, 2, 4, 3

Question 64

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

A)they are species specific.
B)they always lead to the same cellular response.
C)they amplify the original signal manyfold.
D)they counter the harmful effects of phosphatases.
E)the number of molecules used is small and fixed.

Question 65

Which of the following is true during a typical cAMP-type signal transduction event?

A)The second messenger is the last part of the system to be activated.
B)The 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.
E)cAMP is waiting in the cell ready for the signal to be transduced.

Question 66

Lipid-soluble signalling molecules,such as testosterone,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)most cells lack the Y chromosome required.
D)only target cells possess the cytosolic enzymes that transduce the testosterone.
E)only in target cells is testosterone able to initiate the phosphorylation cascade leading to activated transcription factor.

Question 67

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

A)at the exterior surface
B)at the cytosol surface
C)connected with the loop at H5 and H6
D)between the membrane layers
E)there is no carboxyl end in proteins

Question 68

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

A)The ligand will attach to those beads that have the receptor and remain on the column.
B)The ligand will cause the receptor to be displaced from the beads and eluted out.
C)The ligand will attach to the bead instead of the receptor.
D)The ligand will cause the bead to lose its affinity by changing shape.
E)The reaction will cause a pH change due to electron transfer.

Question 69

Binding of a signalling 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)phosphorylated receptor tyrosine kinase dimer
D)ligand-gated ion channel
E)intracellular receptor

Question 70

Use the following figure to answer the questions below.

The structure labelled A is

A)very small.
B)hydrophilic.
C)hydrophobic.
D)NO.
E)a hormone.

Question 71

Use the following figure to answer the questions below.

In the above diagram,what is the significance of E?

A)It allows the proteins to move away from the initial response site.
B)It allows for amplification of the initial signal.
C)It allows cross-talk with DNA.
D)it provides an alternative pathway for ATP production.
E)It is the protein scaffold that allows enzymes to move.

Question 72

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 when epinephrine and glycogen phosphorylase were combined.
E)Epinephrine was known to have different effects on different types of cells.

Question 73

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

A)molecules of the hormone
B)molecules of purified receptor
C)G proteins
D)assorted membrane proteins
E)hormone-receptor complexes

Question 74

Which of the following statements correctly describes quorum sensing?

A)cell-cell communication
B)allows cells to act asynchonously
C)recent evolutionary feature
D)allows organisms to undergo apoptosis
E)always involves cells of the opposite sex.

Question 75

Apoptosis involves all but which of the following?

A)fragmentation of the DNA
B)cell-signalling pathways
C)activation of cellular enzymes
D)lysis of the cell
E)digestion of cellular contents by scavenger cells

Question 76

Which of the following poses 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 may undertake 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.
E)Signals in bacteria are hydrophobic and do not require a cell surface receptor.

Question 77

Use this information to answer the following questions.
Affinity chromatography is a method that can be used to purify cell-surface receptors,while they retain their hormone-binding ability.A ligand (hormone)for a receptor of interest is chemically linked to polystyrene beads.A solubilized preparation of membrane proteins is passed over a column containing these beads.Only the receptor binds to the beads.
What might be one approach to design a drug to maintain low blood sugar levels?

A)activate epinephrine receptors
B)increase cAMP production in liver cells
C)block G protein activity in liver cells
D)increase phosphorylase activity
E)increase membrane fluidity

Question 78

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

A)the exterior (cytoplasmic)end of the receptor
B)the cytosolic end of the receptor
C)the phospholipid's transmembrane domain
D)the amino acid sequence in the binding site for the G protein
E)the amino acids in the binding site for the transduction molecules

Question 79

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

A)at the NH₃ end.
B)at the COO- end.
C)along the exterior margin.
D)along the interior margin.
E)at the loop between H5 and H6.

Question 80

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
E)G protein-coupled receptor