Deck 4: The Structure and Function of the Plasma Membrane

Question 1

What kind of membrane protein is found entirely outside the bilayer on either the extracellular or cytoplasmic surface and is 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

Answer 1

B

Question 2

Figure 4.12 shows the oligosaccharides attached to membrane lipids thus forming gangliosides that determine the A, B and O blood groups. Which statement regarding the arrangement of sugars is INCORRECT?

A)A person with O blood type would have gangliosides with terminal fucose residues only exposed on their glycolipids.
B)A person with A blood type would have gangliosides with both terminal fucose and terminal N-acetylgalactosamine residues exposed on their glycolipids.
C)A person with B blood type would have gangliosides with terminal fucose and galactose residues on their glycolipids.
D)A person with AB blood type would have gangliosides with terminal fucose, terminal N-acetylgalactosamine and terminal galactose residues exposed on their glycolipids.
E)all statements are correct

Answer 2

E

Question 3

Why might integral membrane proteins be difficult to study based upon what you know of their amino acid composition?

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 too small.
D)They are too large.
E)None of these are correct.

Answer 3

A

Question 4

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.

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

Question 5

Which technique allows an investigation of the microheterogeneity of a membrane so that one can see localized differences in protein distribution within membranes?

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

Question 6

People who have the O blood type possess ________.

A)an enzyme that adds an N-acetylgalactosamine to the end of the oligosaccharide chain on RBC membrane glycolipids
B)an enzyme that adds a galactose to the end of the oligosaccharide chain on RBC membrane glycolipids
C)an enzyme that adds phospholipids to the end of the oligosaccharide chain on RBC membrane glycolipids
D)no enzymes capable of attaching galactose or N-acetylgalactosamine to the end of the oligosaccharide chain on RBC membrane glycolipids
E)both an enzyme that adds an N-acetylgalactosamine to the end of the oligosaccharide chain on RBC membrane glycolipids and an enzyme that adds a galactose to the end of the oligosaccharide chain on RBC membrane glycolipids

Question 7

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

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

Question 8

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)More lipid-soluble solutes entered root hair cells faster than polar solutes.
D)Membranes dissolved in gasoline.
E)Membranes did not dissolve in water.

Question 9

Which of the following is NOT a function of membranes?

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

Question 10

Which of the following is a function of membranes?

A)compartmentalization
B)creating a selectively permeable barrier
C)mediating intercellular interactions
D)helping cells respond to external stimuli
E)all of these are correct choices

Question 11

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 to the enzyme 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

Question 12

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 13

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 14

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

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

Question 15

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)malformed glycolipids can cause neurological disease
B)mice with missing glycolipids had muscular tremors
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

Question 16

Gorter and Grendel extracted lipids from human red blood cells. They calculated the total surface area for these red blood cell lipids and found it to be 36 µm². How much surface area would these lipids cover once they were spread across the surface of water?

A)72 µm²
B)36 µm²
C)18 µm²
D)144 µm²
E)30 µm²

Question 17

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 to the enzyme 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 likely to have a cytosolic domain and be exposed only on the interior of the cell?

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

Question 18

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 19

People who have the A blood type possess ________.

A)an enzyme that adds an N-acetylgalactosamine to the end of the oligosaccharide chain on RBC membrane glycolipids
B)an enzyme that adds a galactose to the end of the oligosaccharide chain on RBC membrane glycolipids
C)an enzyme that adds phospholipids to the end of the oligosaccharide chain on RBC membrane glycolipids
D)no enzymes capable of attaching galactose or N-acetylgalactosamine to the end of the oligosaccharide chain on RBC membrane glycolipids
E)both an enzyme that adds an N-acetylgalactosamine to the end of the oligosaccharide chain on RBC membrane glycolipids and an enzyme that adds a galactose to the end of the oligosaccharide chain on RBC membrane glycolipids

Question 20

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

A)They were not stable enough to last until their target destination.
B)Immune system phagocytes removed them from the bloodstream before they could exert an effect.
C)They could not hold water soluble and lipid soluble drugs.
D)They were targeted incorrectly.
E)They expanded osmotically and lysed before reaching their target.

Question 21

On average, how many amino acids, forming a hydrophobic $\alpha$ -helix, 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 22

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 23

Which enzyme releases certain membrane proteins from a membrane and was instrumental in the discovery of GPI-anchored proteins?

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

Question 24

What technique 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

Question 25

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 hydropathy
C)hydropathy plots
D)electron paramagnetic resonance (EPR)spectroscopy
E)infrared spectroscopy

Question 26

How was the asymmetry of membrane lipids discovered?

A)visualization in the electron microscope
B)observationwith 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 27

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 and membrane fusion
E)both membrane budding and membrane fusion

Question 28

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 29

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

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

Question 30

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 31

Using the nucleotide sequence of a gene, which of the following can be learned from a computer-based (computational)analysis of the primary amino acid structure of a membrane protein?

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

Question 32

What 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 33

What technique utilizes the properties of nitroxides to be sensitive to the distance that separates them and an unpaired electron?

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

Question 34

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

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

Question 35

Which of the following is NOT an observed function of peripheral proteins?

A)mechanical support for membrane
B)enzyme activity
C)receptor activity
D)anchor for integral proteins
E)factors that transmit transmembrane signals

Question 36

An 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 attachment of a nitroxide group which can be used to detect position The amino acid substituted is:____________________.

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

Question 37

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)The cell has the ability to maintain 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 38

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 39

Enzymes which play a role in maintaining cellular integrity by stabilizing membrane fluidity include all of the following EXCEPT:

A)dehydrogenases
B)desaturases
C)phospholipases
D)acyltransferases
E)phospholipid synthesizing enzymes

Question 40

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 41

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 42

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 43

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

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

Question 44

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)It moves at a much faster rate than the wild type protein.
B)It moves at a much slower rate than the intact protein.
C)It does not move at all.
D)It is not inserted into the membrane so nothing can be learned about their mobility.
E)It flips to the opposite leaflet.

Question 45

Concentrated areas of sphingolipids and cholesterol that are more gelated and ordered than the surrounding fluid membrane are called ______________ .

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

Question 46

Why would a transverse diffusion or flip-flop of membrane phospholipids from one leaflet to the other be so rare?

A)Flippases are enzymes which are transiently stable and expressed at low concentrations.
B)For flip-flop to occur, it would be necessary for the hydrophilic head of a phospholipid to move through the hydrophobic part of the bilayer, an extremely unlikely event.
C)For flip-flop to occur, it would be necessary for the hydrophobic head of a phospholipid to move through the hydrophilic part of the bilayer, an extremely unlikely event.
D)Other membrane activities like flexing and lateral shift inhibit phospholipid flip-flop.

Question 47

_________ 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 48

You fuse a mouse cell and a human cell and then treat the cell with anti-mouse or anti-human protein-directed antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins show green fluorescence; antibodies to human proteins show red fluorescence). What does the cell look like after one hour?

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 49

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 50

Which substance will cross a plasma membrane most effectively?

A)Molecule AA with an octanol-water partition coefficient of 5
B)Molecule AB with an octanol-water partition coefficient of 0.5
C)Molecule AC with an octanol-water partition coefficient of 50
D)Molecule AD with an octanol-water partition coefficient of 0.05

Question 51

Why are proteins separated on an SDS polyacrylamide gel equally attracted 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 52

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 53

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)It moves much greater distances than the intact protein.
B)It moves much smaller distances than the intact protein.
C)It does not move at all.
D)It is not inserted into the membrane so nothing can be learned about their mobility.
E)It flips to the opposite leaflet.

Question 54

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 55

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 56

You fuse a mouse cell and a human cell and then treat the cell with anti-mouse or anti-human protein-directed antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins show green fluorescence; antibodies to human proteins show red fluorescence). 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 57

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 58

_________ is a technique that 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.

A)FRAP
B)SPT
C)fluorescence recovery after photobleaching
D)optical tweezer manipulation
E)SDS-PAGE

Question 59

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 60

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

A)able to establish and maintain membrane lipid asymmetry
B)interact with neighboring epithelial cells, or the basal membrane
C)block post-synaptic membrane signals
D)transport proteins across the membrane
E)all of the above

Question 61

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 62

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 methylated during the cycle.
E)It must be acetylated during the cycle.

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

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 65

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 66

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 67

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 68

Where is the neuron cell nucleus located?

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

Question 69

Which disease 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 70

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 71

Impulse propagation by a myelinated axon is called ____________ conduction.

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

Question 72

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

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

Question 73

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 74

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

Question 75

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 76

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)an active antiport
B)an active uniport
C)a passive antiport
D)an active symport
E)a passive symport

Question 77

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

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

Question 78

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 79

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 80

What is thought to cause the 1 ms inactive time after a sodium channel initiates an action potential?

A)a higher positive charge
B)a higher negative charge
C)the presence of an inactivating peptide in 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