Deck 4: The Structure and Function of the Plasma Membrane

Question 1

Why did liposomes not work against diseases as hoped when they were first tried?

A)They were degraded in the bloodstream.
B)Immune system phagocytes removed them from the bloodstream before they could exert an effect.
C)They leaked before getting to their target.
D)They were targeted incorrectly.
E)They expanded osmotically and lysed before reaching their target.

Answer 1

B

Question 2

What technique below is often used to identify transmembrane segments of integral proteins?

A)Lineweaver-Burk plot
B)Michaelis-Menten plot
C)hydrophilicity plot
D)hydropathy plot
E)titration plot

Answer 2

D

Question 3

Glycolipids have been shown to play roles in certain disease states in humans and other mammals.Which of the situations below illustrate the ways in which this can happen?

A)failure to add a sugar to the glycolipid.
B)inhibition of glycolipid synthesis.
C)they are the site at which bacterial toxins like those that cause botulism and cholera first bind cells.
D)they are the site at which the influenza virus first binds a cell.
E)All of these are correct.

Answer 3

E

Question 4

Which of the following is not a function of membranes?

A)transporting solutes
B)scaffold for biochemical activities
C)energy transduction
D)signal transition
E)signal transduction

Question 5

What technique allows an investigation of the microheterogeneity of a membrane so that one can see localized differences in different parts of the membrane?

A)freeze-denture replication
B)freeze-fracture replication
C)X-ray crystallography
D)circular dichroism
E)tasty-freeze replication

Question 6

What word describes a molecule that contains both hydrophilic and hydrophobic portions?

A)amphoteric
B)ambidextrous
C)amphipathic
D)rings
E)straight

Question 7

Why are integral membrane proteins difficult to study?

A)They are difficult to isolate in soluble form due to their hydrophobic transmembrane domains.
B)They are difficult to isolate in soluble form due to their hydrophilic transmembrane domains.
C)They are so small.
D)They are so large.
E)None of these are correct.

Question 8

What word below characterizes the amino acids that are found in an $\alpha$ -helical segment that spans a membrane?

A)exclusively circular
B)predominantly hydrophilic
C)predominantly hydrophobic
D)predominantly antiparallel
E)totally parallel

Question 9

You treat some cells with a proteolytic enzyme that is too large to penetrate the cell membrane (Set 1).Another group of cells is made permeable before treatment with the enzyme (Set 2).A third set of cells was not treated with the enzyme at all (controls).Proteins are then extracted from the three different sets of cells and applied to an SDS-PAGE gel.Protein W migrates to the same distance on a gel of proteins from Set 1 and Set 2;Protein W migrates a shorter distance on gels of proteins extracted from the control group than on gels of proteins extracted from Set 1 and Set 2 treated cells.Protein X migrates to the same distance on a gel of proteins from control cells and the gels of the proteins from Set 1 and Set 2.Protein Y migrates a longer distance when extracted from Set 1 cells than does protein Y in the controls;Protein Y moves an even larger distance in the gel of the extracts from Set 2.Protein Z migrates the same distance on gels of proteins from the controls and the proteins extracted from Set 1,but it migrates a longer distance in extracts from Set 2 cells.Which protein is exposed only on the exterior of the cell?

A)Protein W
B)Protein X
C)Protein Y
D)Protein Z
E)Protein K

Question 10

What did Davson and Danielli add to their model of enzyme structure to explain the passage of polar solutes and ions through the membrane and to account for their selective permeability?

A)They proposed protein-lined pores.
B)They proposed lipid-lined pores.
C)They proposed carbohydrate-lined pores.
D)They proposed a protein coating on the cytoplasmic surface of the membrane.
E)They proposed a carbohydrate coating on the external surface of the membrane.

Question 11

On average,how many amino acids engaged in predominantly hydrophobic $\alpha$ - helices does it take to cross the hydrophobic part of the membrane?

A)about 10 amino acids
B)about 20 amino acids
C)at least 40 amino acids
D)about 2 - 3 amino acids
E)None of these are correct.

Question 12

What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?

A)integral protein
B)lipid-anchored protein
C)peripheral proteins
D)phosphatidylcholine
E)galactocerebroside

Question 13

Which of the following is a function of membranes?

A)compartmentalization
B)selectively permeable barrier
C)mediates intercellular interactions
D)helps cells respond to external stimuli
E)All of these are correct.

Question 14

Once the structure of one member of a membrane protein family has been determined,researchers can usually apply a strategy called __________ to learn about the structure and activity of other members of the family.For example,solution of the structure of the bacterial potassium channel KcsA provided a lot of data that could be applied to the structure and mechanism of action of the much more complex eukaryotic potassium channels.

A)heterology modeling
B)homology mapping
C)homology modeling
D)protein mapping
E)homologous characterization

Question 15

How are the new "stealth liposomes" protected from immune system phagocytes?

A)They are kept cold before use.
B)They are coated with carbohydrates.
C)They are given a synthetic polymer coating that protects them from immune destruction.
D)They are loaded with radioactive isotopes.
E)They are colored red.

Question 16

What are the building blocks of a phosphoglyceride,specifically phosphatidic acid?

A)glycerol + 2 phosphate groups + 1 fatty acid
B)glycerol + 1 phosphate group + 2 fatty acids
C)glycerol + 1 phosphate group
D)glycerol + 3 fatty acids
E)glycerol + 1 phosphate group + 3 fatty acids

Question 17

Which protein in the Question above is likely to be buried within the membrane?

A)Protein W
B)Protein X
C)Protein Y
D)Protein Z
E)Protein A

Question 18

What kind of membrane protein is found entirely outside the bilayer on either the extracellular or cytoplasmic surface? These proteins are covalently linked to a membrane lipid situated within the bilayer.

A)integral protein
B)lipid-anchored protein
C)peripheral proteins
D)carbohydrate-anchored protein
E)transmembrane

Question 19

What evidence convinced Overton that membranes were composed of lipids?

A)He could see the lipids in the microscope.
B)Membranes were destroyed by enzymes that degraded lipids.
C)He found that more lipid-soluble solutes enter root hair cells faster than polar solutes.
D)Membranes dissolved in gasoline.
E)Membranes did not dissolve in water.

Question 20

What kind of membrane protein penetrates into the hydrophobic part of the lipid bilayer?

A)integral protein
B)lipid-anchored protein
C)peripheral proteins
D)transmembrane protein
E)both integral protein and transmembrane protein

Question 21

Phosphatidylethanolamine is concentrated in the inner leaflet of the plasma membrane and tends to promote the curvature of the membrane,which is important in _________.

A)membrane budding
B)membrane fragmentation
C)membrane fusion
D)signal transduction
E)both membrane budding and membrane fusion

Question 22

The temperature at which a lipid bilayer shifts from a fluid state to a crystalline gel is called the _____.

A)transition temperature
B)temperature optimum
C)transition series
D)pH optimum
E)gelation temperature

Question 23

What amino acid is made to replace another amino acid in membrane-spanning $\alpha$ -helices by site-directed mutagenesis of the gene coding for the protein? This is done in order to determine how close together two such $\alpha$ -helices are in the structure of an integral protein.The amino acid is added to facilitate the formation of crosslinks between $\alpha$ -helices that are in close proximity.

A)phenylalanine
B)alanine
C)cysteine
D)methionine
E)proline

Question 24

Which of the following cell processes depend on the movement of membrane components and would probably not be possible if membranes were rigid,nonfluid structures?

A)cell movement
B)cell division
C)formation of intercellular junctions
D)endocytosis
E)All of these are correct.

Question 25

They are more gelated and highly ordered than the surrounding more fluid and disordered regions in artificial membranes that consist primarily of phosphoglycerides.They contain higher concentrations of sphingolipids and cholesterol and certain proteins become concentrated within them.What are they?

A)lipid islands
B)collections
C)lipid rafts
D)lipid domains
E)dense bilayers

Question 26

Which of the following can be learned from a computer-based (computational)analysis of the amino acid sequence of a membrane protein,which can be readily deduced from the nucleotide sequence of its isolated gene?

A)its structure
B)its color
C)its orientation within the lipid bilayer
D)its population in each cell
E)both its structure and its orientation within the lipid bilayer

Question 27

Which of the following is not a potential biological role of the lipid asymmetry of the plasma membrane?

A)The glycolipids in the outer leaflet of the membrane may serve as receptors.
B)The presence of phosphatidylinositol primarily in the inner leaflet is involved in signal transduction.
C)Maintenance of a charge differential in the two membrane leaflets.
D)Appearance of phosphatidylserine on the outer surface of aging lymphocytes marks them for destruction by macrophages.
E)Phosphatidylserine on the surface of platelets serves as a signal for blood solubilization.

Question 28

What directly or indirectly determines the transition temperature?

A)the ability of lipid molecules to be packed together
B)whether the fatty acid chains of the lipids are saturated or unsaturated
C)the extent to which the fatty acid chains of the lipids contain double bonds
D)the length of the fatty acid chains
E)All of these are correct.

Question 29

A procedure in which the gene for an integral membrane protein is altered in such a way that the spatial relationships between some of the amino acids in the protein can be revealed is called ________.

A)site-directed mutagenesis
B)site-directed amenuensis
C)hydropathy plots
D)electron paramagnetic resonance (EPR)spectroscopy
E)infrared spectroscopy

Question 30

What technique can clarify the dynamic events that occur as a protein functions by introducing into the protein chemical groups (called nitroxides)that contain an unpaired electron? The properties of these nitroxides are sensitive to the distance that separates them and the unpaired electron produces a characteristic spectrum that can be monitored by the technique in question.The technique yields information about the distance between selected protein residues.

A)site-directed mutagenesis
B)site-directed amenuensis
C)hydropathy plots
D)electron paramagnetic resonance (EPR)spectroscopy
E)infrared spectroscopy

Question 31

Hemolytic anemias are characterized by fragile,abnormally shaped erythrocytes;the disease has been traced to mutations in ________.

A)actin
B)ankyrin
C)hemoglobin
D)spectrin
E)both ankyrin and spectrin

Question 32

While culturing some cells,you lower the temperature of the culture.What happens immediately to the membrane fluidity?

A)Nothing happens.
B)The membrane becomes less fluid.
C)The membrane becomes more fluid.
D)The membrane fluidity fluctuates back and forth from high to low.
E)The membrane fluidity fluctuates back and forth from low to high.

Question 33

Which of the following genetic diseases is characterized by fragile,abnormally shaped erythrocytes and has been traced to mutations in ankyrin or spectrin?

A)hemophilia
B)sickle cell anemia
C)hemolytic anemias
D)leukemia
E)erythroblastosis

Question 34

Enzymes that move certain phospholipids between leaflets have also which of the following properties?

A)Play a role in establishing and maintaining membrane lipid asymmetry
B)Interacts with neighboring epithelial cells,or the basal membrane
C)Blocks post-synaptic membrane
D)Transport proteins
E)All of the above

Question 35

How was the asymmetry of membrane lipids discovered?

A)The lipid asymmetry was visualized in the electron microscope.
B)The lipid asymmetry was observed with a special stain in the light microscope.
C)Treatment of intact red blood cells with phospholipases.
D)Treatment of intact red blood cells with trypsin.
E)Treatment of liver cells with phospholipases.

Question 36

What property of membranes allows interactions to take place within the membrane,including the assembly of membrane protein clusters at particular sites and the formation of specialized structures?

A)hydrophobicity
B)hydrophilicity
C)membrane fluidity
D)their amphipathic nature
E)their amphoteric nature

Question 37

When membrane lipids are extracted from cells and used to prepare artificial lipid bilayers,cholesterol and sphingolipids tend to self-assemble into ________ that are more gelated and highly ordered than surrounding regions consisting primarily of _________.

A)macrodomains,phosphoglycerides
B)microdomains,integral proteins
C)microdomains,phosphoglycerides
D)liquid crystals,phosphoglycerides
E)liquid crystals,microdomains

Question 38

You have fused a mouse cell and a human cell and then treated the cell with specific antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins - green;antibodies to human proteins - red).What does the cell look like immediately after fusion?

A)The cell is half red and half green.
B)The red and green labels are uniformly distributed across the entire membrane.
C)The red and green labels are distributed in intermingled patches.
D)The cell appears to be yellow in color.
E)The cell appears to be brown in color.

Question 39

Which of the following is not a function of peripheral proteins?

A)mechanical support for membrane
B)enzymes
C)receptors
D)anchor for integral proteins
E)factors that transmit transmembrane signals

Question 40

What enzyme was instrumental in the discovery of GPI-anchored proteins? It was found that this enzyme would release certain membrane proteins from a membrane.

A)phospholipase
B)lipase
C)hydroxyurease
D)protease
E)trypsin

Question 41

A transport system that moves one solute into the cell and another one out of the cell during a single cycle accompanied by the expenditure of energy through ATP hydrolysis could be called a(n)_______

A)active antiport
B)active uniport
C)passive antiport
D)active symport
E)passive symport

Question 42

Which proteins move the farthest during SDS-polyacrylamide gel electrophoresis?

A)the largest
B)the smallest
C)the most negative
D)the most positive
E)both the largest and the most negative

Question 43

Usually,optical tweezers drag integral proteins a limited distance before they encounter a barrier that causes their release;upon release,they typically spring backward.What does this suggest?

A)the presence of solid barriers
B)the presence of elastic barriers
C)the attachment of the proteins to the cytoskeleton
D)the attachment of the proteins to the endoplasmic reticulum
E)the presence of rubber in the membrane

Question 44

Which protein in the red blood cell membrane appears to be responsible for the exchange of bicarbonate ions and chloride ions across the red blood cell membrane?

A)glycophorin A
B)glycophorin D
C)band 3
D)glyceraldehyde 3-phosphate
E)alpha-actinin

Question 45

Which protein(s)below is(are)thought to be involved in and influence the stability of red blood cell membranes and the cells themselves by imparting strength,elasticity,and pliability to the membrane?

A)actin and tropomyosin
B)spectrin
C)band 3
D)ankyrin
E)All of these are correct.

Question 46

What happens to phospholipid mobility when the cell is treated with agents that disrupt the underlying membrane skeleton?

A)Their mobility is unchanged.
B)Their mobility is increased because the fences that normally restrict their diffusion are removed.
C)Their mobility is decreased because the fences that normally restrict their diffusion are removed.
D)Their mobility is increased because the treatment raises the temperature.
E)Their mobility is decreased because the treatment lowers the temperature.

Question 47

A channel that opens in response to the binding of a specific molecule,which is usually not the solute that passes through the channel is called a ________.

A)voltage-gated channel
B)charge-gated channel
C)ligand-gated channel
D)positive-gated channel
E)electric-gated channel

Question 48

The movement of water through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration is called ________.

A)diffusion
B)osmosis
C)denaturation
D)metabolism
E)solubility

Question 49

What is thought to be important in maintaining the native structure of the Kv channel membrane protein and promoting its function as a voltage-gated channel.

A)negatively charged cholesterol
B)positively charged sphingolipids
C)negatively charged phospholipids
D)positively charged phospholipids
E)negatively charged sphingolipids

Question 50

An important aspect of transport by facilitated transporters and pumps is ________.

A)conformational shifts
B)rigidity
C)softness
D) $\alpha$ -helix
E) $\beta$ -pleated sheet

Question 51

Integral membrane proteins have been engineered to lack the portion that normally projects into the extracellular space.When the gene is inserted in cells,what happens to the mobility of this protein in the membrane?

A)They move at a much greater rate than the wild type protein.
B)They move at a much smaller rate than the intact protein.
C)They do not move at all.
D)They are not inserted into the membrane so nothing can be learned about their mobility.
E)They flip to the opposite leaflet.

Question 52

In the Na+/glucose cotransporter,_____ moving down its gradient drives the transport of _____ against its gradient.

A)Na+ ions,K+ ions
B)Na+ ions,glucose
C)glucose,Na+ ions
D)glucose,K+ ions
E)K+ ions,glucose

Question 53

_________ can be used to trap integral proteins and drag them through the membrane with a known force,using forces generated by a focused laser beam.This yields information about the presence of membrane barriers.

A)FRAP
B)SPT
C)Fluorescence recovery after photobleaching
D)Optical tweezers
E)SDS-PAGE

Question 54

The sodium-potassium pump makes the cell interior more ______ by pumping ____ sodium ions out of the cell for every ____ potassium ions pumped in.

A)negative,3,2
B)negative,2,3
C)positive,3,2
D)positive,2,3
E)negative,4,3

Question 55

You modify the gene for an integral membrane protein so that the cytoplasmic portions of the protein are deleted.When the gene is inserted in cells,what happens to the mobility of this protein in the membrane?

A)They move much greater distances than the intact protein.
B)They move much smaller distances than the intact protein.
C)They do not move at all.
D)They are not inserted into the membrane so nothing can be learned about their mobility.
E)They flip to the opposite leaflet.

Question 56

Why are the proteins being separated on an SDS polyacrylamide gel attracted equally to the positive electrode?

A)They carry a relatively uniform positive charge distribution
B)They carry a relatively uniform negative charge distribution.
C)They are all the same molecular weight.
D)They are all the same size.
E)They all have the same degree of hydrophobicity.

Question 57

_________ is the movement of a substance from an area of high concentration to an area of lower concentration.

A)Denaturation
B)Osmosis
C)Diffusion
D)Transport
E)Defusion

Question 58

What is the distinguishing characteristic of a P-type pump?

A)It must be pumped during the cycle.
B)It must be phosphorylated during the cycle.
C)It must be protonated during the cycle.
D)It must be deprotonated during the cycle.
E)It must be potassiumated during the cycle.

Question 59

A channel that opens in response to changes in ionic charge across a membrane is called a ________.

A)voltage-gated channel
B)charge-gated channel
C)ligand-gated channel
D)positive-gated channel
E)electric-gated channel

Question 60

Diffusion during which the substance to be transported binds selectively to a membrane-spanning protein,which helps the process along,is called ________.

A)osmosis
B)facilitated osmosis
C)simple diffusion
D)facilitated diffusion
E)active transport

Question 61

Synaptic malfunction or dysfunction may cause which of the following diseases?

A)myasthenia gravis
B)Parkinson's disease
C)schizophrenia
D)depression
E)All of these are correct.

Question 62

______ trigger fusion of synaptic vesicles with the synaptic membranes of the presynaptic cell.This same stimulus also triggers ________.

A)Ca2+ ions,exocytosis
B)Ca2+ ions,endocytosis
C)acetylcholine,exocytosis
D)acetylcholine,endocytosis
E)Na+ ions,exocytosis

Question 63

How do Na+ ions enter a neuron when an action potential is initiated?

A)the Na+/K+-ATPase
B)a gated Na+ pump
C)a voltage-gated Na+ channel
D)the ligand-gated Na+ channel
E)a voltage-gated Na+ facilitated transporter

Question 64

What is caused by the inability of Na+ ion channels to open for several milliseconds after their inactivation?

A)hyperpolarization
B)depolarization
C)termination
D)a refractory period
E)an action potential

Question 65

Tetrahydrocannabinol,the active ingredient in marijuana,binds to receptors located in the ________ terminals of certain brain neurons.It lowers the likelihood that these neurons will release ________.

A)postsynaptic,neurotransmitters
B)presynaptic,neurotransmitters
C)presynaptic,Ca2+ ions
D)postsynaptic,Ca2+ ions
E)dendritic,neurotransmitters

Question 66

The ability,possessed by all organisms,to respond to external stimulation is known as _______.

A)excitation
B)irritability
C)irritation
D)irrigation
E)irrigatability

Question 67

Which site in a neuron receives incoming information from external sources?

A)Dendrites
B)Axon
C)Axon hillock
D)Terminal knob
E)Cell body

Question 68

Impulse propagation by a myelinated axon is called ________ conduction.

A)saltatory
B)myelinated
C)rapid fire
D)jump stop
E)leap frog

Question 69

What is thought to cause the sodium channels that initiate an action potential to be inactivated for a brief time after being open for about 1 msec?

A)a higher positive charge
B)a higher negative charge
C)the random diffusion of an inactivation peptide into the opening of the channel pore
D)removal of a peptide from the channel protein
E)covalent addition of a peptide to the cytoplasmic end of the channel protein

Question 70

Long-term potentiation is associated with NMDA receptors,one of several types of receptors that bind to the excitatory neurotransmitter _______.Its binding opens an internal cation channel within the receptor that allows _____ influx into the postsynaptic neuron,triggering a cascade of biochemical changes that lead to synaptic strengthening.

A)GABA,Ca2+ ion
B)glutamate,Ca2+ ion
C)glutamate,K+ ion
D)GABA,K+ ion
E)acetylcholine,Ca2+ ion

Question 71

As an action potential is initiated,the membrane is ______.This is caused by the ____ of ____ ions.

A)hyperpolarized,efflux,Na+
B)depolarized,influx,Na+
C)depolarized,influx,K+
D)hyperpolarized,influx,Na+
E)depolarized,efflux,Na+

Question 72

Where in a myelinated axon are nearly all of the ion channels concentrated?

A)the cell body
B)nodes of Ranvier
C)dendrites
D)axon terminals
E)neuron nucleus

Question 73

___________ is a process that strengthens certain synapses by repeated neuron stimulation over a short time period.

A)Denturation
B)Long term potentiation
C)Short term memory
D)Temporality
E)Long term deviation

Question 74

What causes the membrane potential to return to the normal negative value after an action potential has occurred?

A)opening of a voltage-gated K+ channel
B)opening of a voltage-gated Na+ channel
C)closing of a voltage-gated K+ channel
D)opening of a ligand-gated Na+ channel
E)opening of a voltage-gated K+ facilitated transporter

Question 75

Cocaine acts by _________.

A)enhancing the degradation of acetylcholine.
B)depressing the degradation of acetylcholine
C)interfering with dopamine reuptake from the synaptic cleft
D)enhancing dopamine reuptake from the synaptic cleft
E)destroying dopamine in the synapse

Question 76

How is a nerve impulse usually transmitted across a synapse from a presynaptic to a postsynaptic cell?

A)via a direct connection
B)via a spark
C)via a neurotransmitter
D)via Na+ ions
E)via plasmodesmata

Question 77

Which disease below is caused by the deterioration of the myelin sheath?

A)myasthenia gravis
B)multiple sclerosis
C)muscular dystrophy
D)diabetes mellitus
E)lupus erythematosus

Question 78

Which part of a neuron conducts impulses away from the cell body toward the target cell(s)?

A)axon hillock
B)cell body
C)dendrites
D)axon
E)terminal knob

Question 79

Where is the neuron cell nucleus located?

A)axon hillock
B)cell body
C)dendrites
D)axon
E)terminal knob

Question 80

What happens after a subthreshold depolarization?

A)a full action potential
B)a partial action potential
C)no action potential
D)a proportional action potential
E)a reversal of the direction of the neural impulse