Karp's Cell and Molecular Biology: Ch 4. The Structure and Function of the Plasma Membrane Flashcards

Which of the following statements is FALSE about plasma membrane structure?

The membrane is based on a lipid bilayer.
The polar groups on membrane lipids are directed toward the aqueous environment.
The hydrophobic groups on membrane lipids are directed toward one another.
The membrane contains proteins.
The membrane contains a double layer of proteins.

Functions of cell membranes include all but which one of the following?

Determining what can enter or leave a cell.
Providing different compartments within the cell that may carry on different activities.
Interacting with other cells.
Responding to stimuli.
Protecting the cell from damage.

Signal transduction:

converts one type of energy to another.
absorbs energy from sunlight and converts it into chemical energy.
involves the response of a cell to external stimuli, such as specific molecules or light.
is mediated by membrane carbohydrates.
has little to no effect on the behavior of a cell.

Which of the following is NOT a function of membranes?

transporting solutes
scaffold for biochemical activities
energy transduction
signal transition
signal transduction

What evidence convinced Overton that membranes were composed of lipids?

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

Gorter and Grendel extracted lipids from human red blood cells. They calculated the total surface area of these red blood cells and found it to be 36 µ². Based on their findings, how much surface area should these lipids cover once they were spread across the surface of water?

72 µ²
36 µ²
18 µ²
144 µ²
30 µ²

What evidence suggested to cell physiologists that there had to be more to the structure of the cell membrane than just a lipid bilayer?

Lipid solubility was not the only factor to determine whether a substance could penetrate the plasma membrane.
Cell membranes were harder than lipid bilayers.
The surface tensions of various cell membranes were calculated to be much lower than those of pure lipid bilayers.
Cell membranes were more fluid than lipid bilayers.
The lipid solubility and surface tensions of natural cell membranes differed significantly from those same properties of lipid bilayers.

What was determined to be a possible explanation for the differences between natural cell membranes and lipid bilayers?

the presence of nucleic acids in the membrane
the presence of proteins in the membrane
the presence of carbohydrates in the membrane
the higher temperature of natural cell membranes
the lipid content of the natural cell membranes as compared to that of lipid bilayers

MOST functions of cell membranes are carried out by:

lipids.
phospholipids.
proteins.
cholesterol.
liposomes.

Which of the following statements is FALSE regarding liposomes?

They are very useful in membrane research.
They form spontaneously when a small amount of phosphatidylcholine is dispersed in an aqueous solution.
They are fluid-filled spherical vesicles.
They can be used to deliver drugs within the body.
They are normally found within the bloodstream of eukaryotes.

Which of the following statements is TRUE regarding phospholipids?

They are amphipathic.
They possess a hydrophobic head group composed of fatty acids.
They possess two charged hydrophilic phosphate groups.
They all include at least one saturated omega-3 fatty acid.
They all possess a positively charged amino group.

Carbohydrates found on the plasma membrane of the red blood cell:

do not determine the blood type of the person.
are determined by the dietary preferences of individuals.
may be related to certain disease conditions.
are added to membrane lipids by mitochondria or chloroplasts.
are not immunogenic.

The ratio of lipids to proteins in a membrane:

is about 50% lipid and 50% protein.
varies considerably depending upon the type of cell and membrane, the organism, and the function of the membrane.
always indicates more lipid in the membrane than protein.
always indicates more protein in the membrane than lipid.
reveals more lipid in the mitochondrial membrane than in the plasma membrane.

Membrane carbohydrates:

comprise about 90% of the molecules in the membrane.
can be covalently linked to membrane proteins or to membrane lipids.
are found on the inner membrane surface where they interact with cellular organelles.
are removed from membranes in the process of glycosylation.
are only present in human red blood cells.

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

glycerol + 2 phosphate groups + 1 fatty acid
glycerol + 1 phosphate group + 2 fatty acids
glycerol + 1 phosphate group
glycerol + 3 fatty acids
glycerol + 1 phosphate group + 3 fatty acids

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

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

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

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

Which of the following statements about membrane proteins is FALSE?

Lipid-anchored proteins are attached to lipids that are situated within the bilayer.
Peripheral proteins provide about 60% of all current drug targets.
Integral proteins have domains that protrude from both the extracellular and the cytoplasmic sides of the membrane.
Integral proteins comprise 25-30% of all encoded proteins.
Peripheral proteins are associated with the surface of a membrane by noncovalent bonds.

Integral membrane proteins are difficult to isolate in a soluble form because:

they are generally denatured by the nonionic (uncharged) detergents often used to remove them from the membrane.
they possess hydrophobic transmembrane domains.
they are not amphipathic.
they are too small.
they are composed of more than one subunit.

Which one of the following statements about peripheral membrane proteins is FALSE?

They can either attach or detach from the membrane as needed.
They provide mechanical support for the membrane.
They may function as enzymes.
They have domains that protrude from both the extracellular and the cytoplasmic sides of the membrane.
They may function as an anchor for integral membrane proteins.

Functions of integral proteins include all but which one of the following?

acting as channels through which substances can pass through the membrane
transporting substances through the membrane
binding to specific ligands that induce a cellular response
interacting directly with cellular DNA
transferring electrons during photosynthesis or respiration

Which one of the following statements is NOT true of nitroxide groups?

They contain an unpaired electron that can be monitored by electron paramagnetic resonance (EPR) spectroscopy.
They can be introduced into the structure of a protein.
They were used to discover the conformational changes that occur in a membrane channel in response to pH changes.
They are used to develop a hydropathy plot that measures the hydrophobicity of amino acids.
They are sensitive to the distance that separates them.

Which of the following statements is NOT true of the freeze-fracture replication technique?

Tissue is frozen solid and then struck with a knife blade, which fractures the block into two pieces.
The fracture plane often follows a path between the two leaflets of the lipid bilayer.
Once membranes are split by the fracturing, metals are deposited on their exposed surfaces to form a replica, which can be viewed in the electron microscope.
Most of the membrane-associated particles visualized by this technique are peripheral membrane proteins
This technique allows investigation of the microheterogeneity of the membrane.

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

about 10 amino acids
about 20 amino acids
at least 40 amino acids
about 2 – 3 amino acids
None of these are correct.

Saturated fatty acids:

have crooked chains where carbon atoms are bonded to one another.
are likely to pack together loosely at low temperature.
have relatively low transition temperatures.
have straight fatty acyl chains.
typically have lower melting points

Lipid rafts:

are easily seen in living cells, but are difficult to re-create in the lab.
may repel some carbohydrates, but attract others.
are thought to be patches of cholesterol and sphingolipids that tend to float within the more fluid environment of phosphoglycerides.
are more disordered than the surrounding phosphoglycerides.
can be used to deliver certain medications.

Membrane fluidity can be increased by all of the following mechanisms EXCEPT:

desaturation of fatty acid chains.
the presence of two unsaturated fatty acid chains in a single phospholipid molecule.
reshuffling of fatty acid chains between glycerol backbones to increase the number of double bonds in the fatty acid chains of membrane phospholipids.
raising the melting temperature of the lipid bilayer fatty acids.
forming double bonds between carbon atoms that comprise the fatty acid chain.

Ankyrin and spectrin are peripheral membrane proteins that:

may cause muscular dystrophy in red blood cells when mutated.
play no role in the development of hemolytic anemias.
play a major role in determining the biconcave shape of the erythrocyte.
form a supportive fibrillar skeleton linked by strong covalent bonds.
facilitate movement of membrane proteins.

The major drawback of using fluorescence recovery after photobleaching (FRAP) to follow the movements of molecules in the membranes of living cells is:

it can only be used to follow the average movements of a relatively large number of molecules over a relatively large distance.
it cannot be used to determine the rate of diffusion.
it does not allows an accurate determination of the percentage of labeled molecules that are free to diffuse.
it requires an electron microscope.
it can cause blindness in the researcher.

The plasma membrane of the human erythrocyte is the MOST studied and BEST understood of all the diverse types of membrane because:

red blood cells are expensive to obtain and present as a low abundance cell within blood.
it is easily obtained by hemolysis of red blood cells.
red blood cells are abundant in lymphatic fluid as well.
a lack of antigenic variation makes all studies uniform in scope.
red blood cell nucleus permits DNA studies to take place.

Individuals that lack glycophorin A in their red blood cell membranes:

typically do not live past infancy.
may be protected from the protozoan that causes malaria.
must be blood type O.
have positively-charged cells.
will react poorly to repeated transfusions of type B blood.

Movement of membrane proteins may be restricted by all of the following EXCEPT:

a high density of neighboring proteins embedded in the membrane.
interactions with the underlying "membrane skeleton."
peripheral proteins situated on the cytoplasmic side of the membrane.
increased temperature.
interaction of integral membrane proteins with extracellular materials..

In the cell fusion experiments of Larry Frye and Michael Edidin of Johns Hopkins University,:

fluorescent dyes were covalently linked to antibodies for membrane proteins.
cells from mice and from humans were fused to each other.
it was shown that membrane proteins could move within the plane of the membrane.
indicated that the mobility of membrane proteins was decreased at lower temperatures.
All of the choices are correct.

Which of these processes REQUIRES input of energy to move materials across a membrane?

Active transport that moves substances against a concentration gradient.
Simple diffusion of glucose through the lipid bilayer.
Diffusion that is facilitated by a protein transporter.
Simple diffusion through an aqueous, protein-lined channel.
Diffusion of chloride ions through the lipid layer.

The substance a-bungarotoxin possesses all of the characteristics EXCEPT that:

it causes paralysis.
it is a component of snake venom.
it binds to nicotinic acetylcholine receptors.
it was used to measure the amount of the acetylcholine receptor purified using affinity chromatography.
it binds to dopaminergic receptors.

Aquaporins:

can be regulated by the hormone vasopressin.
prevent the passage of water through the membrane.
are dependent upon energy from ATP.
are lipid-anchored membrane proteins.
are only present in bacterial cells.

Insulin:

is secreted when the level of blood glucose is low.
stimulates the release of glucose from the cells lining the digestive tract.
moves GLUT4 glucose transporters to the surface of the cell.
phosphorylates sugars after they enter the cytoplasm.
causes the pancreas to release glucose into the bloodstream.

A symport:

involves proteins called exchangers.
is the process used by Na⁺/K⁺ ATPase.
is used to move Na⁺ and glucose together into the epithelial cells of the intestine.
maintains proper pH by coupling movement of Na⁺ and H⁺ ions.
moves two transported molecules in opposite directions.

The best understood gated channel is:

the channel in the inner ear that responds to sound.
an aquaporin.
voltage-gated potassium ion channels.
the ligand-gated nicotinic acetylcholine receptor.
channels in the integument of the model organism C. elegans.

One reason why gene therapy has NOT been successful in the treatment of cystic fibrosis is that:

the defective cells are too distant from the inhaled agents that deliver the normal version of the gene.
adenovirus was not able to achieve genetic modification of the target cells and suppressed the immune response leading to lung inflammation.
adenovirus easily integrated its own DNA into the target cell, and researchers feared this could cause cancer.
adenovirus did not integrate its own DNA into the target cell and had to be re-administered frequently, increasing the risk of an inflammatory response.
liposomes stimulated a destructive immune response.

The sodium-potassium pump, or Na⁺/K⁺ ATPase:

moves Na⁺ ions and K⁺ ions in both directions across the membrane.
moves both Na⁺ ions and K⁺ ions across the membrane against their concentration gradients.
moves both Na⁺ and K⁺ ions into the cell.
pumps both Na⁺ and K⁺ ions out of the cell.
exchanges one ion of Na⁺ for one ion of K⁺ across the membrane.

Claude Bernard's use of curare and John Langley's use of nicotine:

damaged the fibers of skeletal muscle, so that it could not contract.
indicated that a chemical transmitter released from nerve cells had an effect on skeletal muscle cells.
proved that an electrical impulse passed from nerve to muscle.
slowed the rate of beating of a frog's heart.
damaged nerve cells, so that they could not stimulate a muscle to contract.

Which of the following statements is FALSE regarding the diffusion of substances through membranes?

Water can diffuse through the lipid bilayer because it is small.
Substances with a larger partition coefficient are better able to diffuse through the lipid bilayer.
Diffusion across a membrane requires a concentration gradient.
A membrane is permeable to a substance that can cross through the lipid bilayer or through an aqueous pore that spans the membrane.
Glucose passively diffuses into cells where it is used as a nutrient.

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) _______

active antiport
active uniport
passive antiport
active symport
passive symport

Diffusion:

creates a concentration gradient between two regions.
reverses a concentration gradient between two regions.
eliminates a concentration gradient between two regions.
has no effect on the concentration gradient between two regions.
is not dependent upon a concentration gradient between two regions.

An electrochemical gradient:

is determined by the concentration difference of a substance between two compartments.
is determined by the difference in charge between two compartments.
is determined by the concentration difference of a substance between two compartments and by the difference in charge between two compartments.
is neither determined by the concentration difference of a substance between two compartments nor by the difference in charge between two compartments.
cannot be established with substances using electrolytes.

The Na⁺/glucose cotransporter possesses NONE of the listed characteristics EXCEPT:

moves glucose into the cell down its concentration gradient.
is driven by the potential energy stored in the ionic Na⁺ gradient.
moves Na⁺ into the cell in exchange for the outward movement of a molecule of glucose.
is an example of primary active transport.
works for fructose transport as well.

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

negative, 3, 2
negative, 2, 3
positive, 3, 2
positive, 2, 3
negative, 4, 3

Gated channels may be opened or closed by all of the following EXCEPT:

mechanical forces.
voltage differences.
binding of a ligand.
voltage clamping.
All of these can cause opening or closing of channels.

Which organism provided an ideal system for the study of the nicotinic acetylcholine receptor?

frogs
native South American hunters
electric fish
a Taiwanese snake
E. coli

If a red blood cell were added to a hypotonic solution,:

it would rapidly gain water and swell or burst.
it would rapidly lose water and shrink.
nothing much would happen.
solute would leave the cell and enter the more dilute solution.
it is impossible to determine what might happen.

Facilitated diffusion:

requires energy from ATP.
requires a concentration gradient.
occurs by passage directly through the lipid bilayer.
can move substances in only one direction across the membrane.
always shows a direct relationship between the rate of movement of a substance across the membrane and the concentration of the substance to be moved.

Which one of the following statements is FALSE regarding the CFTR protein?

When mutated, the CFTR protein can causes cystic fibrosis.
It is found on epithelial cells.
It acts as a cyclic AMP-regulated chloride channel.
It is important in reducing the viscosity of mucus.
It conducts bicarbonate (HCO₃ ^-) ions.

An action potential is ultimately caused by:

changes in membrane permeability.
maintaining a constant membrane potential.
influx of potassium ions.
efflux of sodium ions.
Na⁺/K⁺ ATPase.

Which one of the following statements regarding the myelin sheath is FALSE?

It slows down propagation of nerve impulses along an axon.
It allows saltatory conduction whereby action potentials are generated only at the nodes of Ranvier.
It deteriorates in those who suffer from multiple sclerosis.
It is composed of layers of lipid-containing membranes.
It is composed of Schwann cells or oligodendrocytes.

Acetylcholine:

excites both skeletal muscle and cardiac muscle.
is the primary inhibitory neurotransmitter in the brain.
binds to the GABA receptor and acts as an anesthetic.
increases in concentration in the synaptic cleft in the presence of drugs that inhibit acetylcholinesterase.
inhibits skeletal muscle activity.

Drugs may affect behavior by having which of these effects at the synapse?

They may prevent the reuptake of neurotransmitters from the synaptic cleft.
They may prevent release of neurotransmitters from the presynaptic cell.
They may block receptors that bind to neurotransmitters.
They may mimic the action of neurotransmitters at the synapse.
Drugs may affect behavior by all of these mechanisms.

Which of the following statements is FALSE regarding synaptic plasticity?

It is most readily observed in studies of neurons from the hippocampus.
It is most important during early adulthood when people are attending college or learning new job skills.
It is a key element in learning and short-term memory.
It can result in long-term potentiation (LTP).
It is a critical developmental phenomenon, but persists to an extent during the lifespan of an organism.

When cation-selective channels open in the postsynaptic cell membrane,:

the cell is inhibited.
the resting membrane potential becomes more negative.
the cell goes through biochemical changes that lead to synaptic strengthening.
an action potential does not occur at the postsynaptic membrane.
K⁺ ions move into the postsynaptic cell, causing depolarization.

Which of the following represents the correct order of changes in membrane permeability that produce an action potential?

increase in K⁺ permeability; increase in Na⁺ permeability
increase in Na⁺ permeability; increase in K⁺ permeability
increase in Na⁺ permeability; decrease in K⁺ permeability
decrease in K⁺ permeability; increase in Na⁺ permeability
increase in Na⁺ permeability; decrease in Na⁺ permeability

When a neuron is at rest,:

it is most permeable to Na⁺ ions.
it is most permeable to K⁺ ions, and they leak out of the cell.
it is most permeable to K⁺ ions, and they leak into the cell.
it is not permeable to either Na⁺ or K⁺ ions.
it is equally permeable to Na⁺ and K⁺ ions.

The strength of a stimulus is encoded in the nervous system by:

the strength of the action potential.
the size of the action potential.
the shape of the action potential.
the size and shape of the action potential.
the frequency of the action potential.

The fine extension of a neuron that conducts impulses away from the cell body is:

an axon.
a dendrite.
a terminal knob.
a myelin sheath.
an action potential.

After a nerve impulse reaches the synaptic knob, the first step in synaptic transmission is:

opening of voltage-gated Ca²⁺ channels.
closing of voltage-gated Ca²⁺ channels.
opening of voltage-gated Na⁺ channels.
activation of the nicotinic acetylcholine receptor.
release of acetylcholine into the synaptic cleft.

The Venus flytrap has a sensory mechanism that responds to a(n) ____________ stimulus by opening ion channels in the plasma membrane and thus depolarizing the membrane.

chemical
electrical
mechanical
photoelectric
sonic

The channels that create the plant action potential accomplish this by allowing the movement of:

Na⁺ ions into the cell cytoplasm.
Na⁺ ions out of the cell.
Cl^- ions out of the cell.
Cl^- ions into the cell cytoplasm.
Ca²⁺ ions into the cell cytoplasm.

Repolarization in plant cells is accomplished by opening channels that allow:

Na⁺ ions to enter the cell.
Na⁺ ions to leave the cell.
Cl^- ions to enter the cell.
Cl^- ions to leave the cell.
K⁺ ions to leave the cell.

How do plant cell action potentials differ from animal cell action potentials?

Plant action potentials last longer.
Plant action potentials propagate more quickly.
Plant action potentials propagate more slowly.
Plant action potentials last longer and propagate more slowly.
Plants action potentials last longer and propagate more quickly.

How does an action potential travel long distances through the plant? How does an action potential travel from cell-to-cell?

An action potential travels long distances through the phloem and from cell-to-cell through cell-cell junctions.
An action potential travels long distances through the xylem and from cell-to-cell along the cell wall.
An action potential travels long distances through the phloem and from cell-to-cell along the cell wall.
An action potential travels long distances through the xylem and from cell-to-cell through cell-cell junctions.
An action potential travels long distances along the cell walls and from cell-to-cell along the cell walls.

Which of the following is a reason that using a glass microneedle to influence the activity of nerve cells in a patient is impractical?

Damage to the cell.
Inability to maintain such an electrode for long periods.
The need to insert the electrode into a cell using a microscope.
All of the procedures are impractical to use in a patient.

What is currently the most successful form of neurotechnology?

prosthetic legs
prosthetic arms and hands
cochlear implants
digital vision aids
olfactory implants

Why must cochlear implants be flexible?

to vibrate appropriately in the presence of sound waves
to bend into the right shape without damaging the organ itself
to fit in the curved area of the pinna of the ear
to fit easily just underneath the ear drum
to connect directly with the part of the brain that interprets sound

Why is the cochlea an excellent candidate for neurotechnology?

Different frequencies of sound are sensed in different regions along the cochlear spiral.
There is a straightforward relationship between the position of a given electrode in the implant and the information it must transmit.
The length of the cochlea allows electrodes to be spaced millimeters apart.
The cochlear implant is much easier to engineer than attempting to make high-density electrode arrays that target individual neurons.
All of the given answers are correct.

What are some possible current and future applications of implanted microelectrode arrays?

to stimulate the retina, the optic nerve, and the visual cortex to provide sight to blind patients
to restore partial hearing to deaf patients by direct stimulation of auditory nerves
to control seizures
to restore movement to paralyzed patients
All of these are possible applications of microelectrode arrays.

The use of microelectrode array implants in the brain is challenging for long periods of time because:

such implants degrade neural tissue
the brain often reacts to the presence of a foreign object by becoming inflamed or forming scar
the brain often reacts to the presence of a foreign object by becoming inflamed
such implants can cause nervous tissue to dedifferentiate
the brain often reacts to the presence of a foreign object by becoming inflamed or forming scars