Chapter 12

What determines the direction that glucose is transported across the membrane, through a glucose transporter? Choose one: membrane potential a molecule's size a molecule's charge concentration gradient

concentration gradient

(Q015) Shown is a diagram of a nerve cell. Which line indicates the location of the dendrites?

2

Which of the following is supported by the information in the figure? Choose one or more:' A.Sodium and potassium are involved in co-transport. B.Glucose enters the cell by simple diffusion. C.Nucleotides enter the cell by facilitated diffusion.

A and

Q009) Which of the following represents a symport transporter protein?

A co-transported ion

(Q001) Which of the following would be able to cross a protein-free lipid bilayer most rapidly? a chloride ion (charged, small) glucose (uncharged polar, large) ethanol (uncharged polar, small) a steroid hormone (nonpolar, large)

a steroid hormone (nonpolar, large)

(Q005) Which factors determine the force driving the passive transport of charged solutes across the membrane? concentration gradient only membrane potential only electrochemical gradient ATP gradient

electrochemical gradient

Which of the following characteristics of aquaporins ensure that the channel selectively transports only water molecules and not other solutes? Choose one or more: A. The channel has a narrow pore that is only wide enough for a single water molecule to pass through. B. Two asparagines in the center of the pore prevent protons from passing through the channel. C.A glutamate at the entrance to the channel prevents positive ions from entering the channel. D.The channel undergoes conformational changes to push water through the channel.

A and B

Which of the following characteristics of K+ channels are important for the selectivity for K+ rather than other ions? Choose one or more: A.Carbonyl groups line the wall of the pore. B.Acidic side chains line the wall of the pore. C.Four rigid protein loops line the narrowest part of the pore. D.Basic side chains line the wall of the pore.

A and C

(Q016) How does an action potential spread along the cell membrane? Potassium leak channels quickly reverse the action potential to move the membrane depolarization away from the original site. A change in membrane potential triggers the opening of nearby voltage-gated sodium channels in a one-way direction. Voltage-gated Ca2+ channels are activated by the action potential and the calcium diffuses along the membrane. The ions entering the cell upon triggering an action potential travel laterally along the membrane to carry the charge.

A change in membrane potential triggers the opening of nearby voltage-gated sodium channels in a one-way direction.

Tetrodotoxin is a potent toxin found in a variety of organisms including the pufferfish. The toxin binds to the extracellular side of the Na+ channel and prevents channel opening. This leads to paralysis of muscles, including the diaphragm. Death from respiratory failure can occur after ingestion of as little as 1 mg of the toxin. Why does this toxin cause paralysis? Choose one: A. The membrane depolarization is not amplified along the axon. B. The Na+ channels remain in the inactive, refractory state. C. The axon membranes become over-depolarized. D. The Na+ channel does not open wide enough to allow enough Na+ through the channel.

A. The membrane depolarization is not amplified along the axon.

(Q007) A sodium-potassium antiport maintains the extracellular concentration of sodium at levels that are about 20-30 times higher than inside the cells. What directly supplies the energy for maintaining this gradient? Potassium supplies the energy, as it is moving along its concentration gradient. Sodium supplies the energy, as it is moving along its concentration gradient. ATP hydrolysis drives the function of the pump. A proton gradient in the mitochondria drives the antiport.

ATP hydrolysis drives the function of the pump.

Why would a cell express the aquaporin protein if water can cross the membrane in the absence of aquaporin? Choose one: A. Aquaporin moves a positively charged ion along with water across the membrane. B. Aquaporin facilitates the faster movement of water molecules across the membrane. C. Aquaporin limits the movement of water molecules so they do not move too quickly across the membrane. D. Water molecules cannot cross the membrane in the absence of a pore like aquaporin.

B. Aquaporin facilitates the faster movement of water molecules across the membrane.

For voltage-gated channels, a change in the membrane potential has what effect on the channel? Choose one: A. It changes the width of the channel opening. B. It alters the probability that the channel will be found in its open conformation. C. It either opens the channel or closes it, depending on the voltage. D. It makes the channel more sensitive to the binding of neurotransmitters. E. It changes which ions can pass through the channel.

B. It alters the probability that the channel will be found in its open conformation.

What is the name of the specialized junction between a neuron and a target cell? Choose one: A. nerve terminal B. synapse C. synaptic vesicle D. axon E. dendrite

B. synapse

During the activation of a neuron, the action potential propagates in only one direction. How is this achieved in the neuron? Choose one:' A. The Na+ channel becomes permanently inactivated after the action potential passes. B. The Na+ channel closes during the action potential and then rapidly returns to the open state after the action potential passes. C. The Na+ channel becomes inactivated and refractory to reopening for a short time after the action potential passes. D. The Na+ channel remains open during the action potential and then rapidly returns to the closed state after the action potential passes.

C. The Na+ channel becomes inactivated and refractory to reopening for a short time after the action potential passes.

Which organelle is important for controlling the concentration of calcium ions in the cytosol?Choose one: A. Golgi apparatus B. lysosome C. endoplasmic reticulum D. nucleus

C. endoplasmic reticulum

Which of the following mechanisms prevents osmotic swelling in plant cells? Choose one: A. the expulsion of water from contractile vacuoles B. turgor pressure C. tough cell walls D. the collection of water in contractile vacuoles E. the activity of Na+ pumps

C. tough cell walls

(Q008) Which of the following ions has a low cytosolic concentration so that a flood of this ion into the cell can be used as a signal for cell processes like fertilization? Ca2+ H+ K+ phosphate

Ca2+

Which is not true about the acetylcholine receptor on vertebrate muscle cells?Choose one: A. Its pore includes negatively charged amino acid side chains at both ends. B. It depolarizes the muscle cell membrane when bound to acetylcholine. C. It does not discriminate between Na+, K+, and Ca2+. D. It is a voltage-gated cation channel. E. Even with acetylcholine bound, it flickers randomly between open and closed states.

D. It is a voltage-gated cation channel.

What is typically true of ion channels? Choose one: A. They hydrolyze ATP B. They are open all the time. C. They are nonselective. D. They are gated. E. They operate by active transport.

D. They are gated.

When a neuron has been stimulated by a signal, the change in membrane potential first spreads locally to adjoining regions of the plasma membrane by what means? Choose one: A. opening of ligand-gated ion channelsB. action potential C. active transport D. opening of voltage-gated ion channels E. passive spread

E. passive spread

To pass through the pore of an ion channel, what must be true of an ion? Choose one: It must surround itself with water molecules. It must avoid contact with the channel wall. It must interact with polar groups in the narrowest part of the channel. It must interact with nonpolar groups in the selectivity filter. It must be positively charged.

It must interact with polar groups in the narrowest part of the channel.

(Q003) Which ion is generally maintained at a high concentration inside the cell and a low concentration outside the cell? Na+ K+ Cl- H+

K+

(Q006) Which of the following is NOT used as a source of energy by a transmembrane pump to actively transport a solute? ATP Na+ H+ K+

K+

In most animal cells, which ion can move through "leak" channels? Choose one: Ca2+ H+ Na+ Cl- K+

K+

Lipid bilayers are highly impermeable to which molecule(s)? Choose one: Na+ and Cl- steroid hormones carbon dioxide oxygen water

Na+ and Cl-

(Q018) What is the role of K+-gated ion channels in an action potential? They lead to the action potential reaching its highest state of cell depolarization. They help reverse the action potential by repolarizing the cell. They do not have a role in action potentials. They provide the energy for the sodium-potassium pump to reestablish resting potential.

They help reverse the action potential by repolarizing the cell.

(Q002) Which of the following is a difference between transporters and channels? Transporters move solutes against their concentration gradient, whereas channels can move solutes with or against their concentration gradient. Channels do not discriminate between ions, whereas transporters bind their solute with extreme specificity. Transporters can facilitate both active or passive transport of solutes; channels facilitate only passive transport. Channels are single-pass transmembrane proteins, whereas transporters are multipass transmembrane proteins.

Transporters can facilitate both active or passive transport of solutes; channels facilitate only passive transport.

(Q019) How is an electrical signal converted to a chemical signal at a nerve terminal? Voltage-gated Ca2+ channels are activated and the influx of Ca2+ triggers the release of neurotransmitters. Ligand-gated channels are bound by ions and open to allow the flow of neurotransmitters out of the cell. Mechanically gated channels change conformation due to the electrical signal and create a mechanical signal. The influx of ions leads to a pH change, chemical transformation, and signaling.

Voltage-gated Ca2+ channels are activated and the influx of Ca2+ triggers the release of neurotransmitters.

(Q014) How are voltage-gated ion channels opened by voltage sensors? Voltage sensors on the channel change their amino acid side chains from positively to negatively charged. When membrane potential changes sufficiently, the electrical force causes voltage sensor domains to change conformation. Ion binding to voltage sensors causes the channel pore to widen and open. Changes in membrane potential lead to increased gene expression of voltage-gated ion channel proteins.

When membrane potential changes sufficiently, the electrical force causes voltage sensor domains to change conformation.

The movement of an ion against its concentration gradient is called what? Choose one: passive transport facilitated diffusion osmosis active transport

active transport

Inhibitory neurotransmitters such as glycine and GABA make a postsynaptic cell harder to depolarize by allowing what? Choose one :an influx of K+ the escape of Na+ an influx of Cl- an influx of Na+

an influx of Cl-

Glucose enters the cell by which process? Choose one: osmosis facilitated diffusion simple diffusion active transport

facilitated diffusion

(Q010) What is responsible for moving glucose from the gut lumen into intestinal epithelial cells? uniport glucose transporter glucose-sodium symport glucose-sodium antiport passive diffusion

glucose-sodium symport

Q017) What is the conformation of the voltage-gated Na+ channel that keeps the action potential from traveling backward along the axonal membrane? inactivated open closed triggered

inactivated

(Q012) An extracellular molecule binds to a channel and triggers it to move more often to the open conformation than the closed conformation, as shown in the figure. This is referred to as a ___________ channel.

ligand-gated

What is the voltage difference across a membrane of a cell called? Choose one: electrical current membrane potential gradient establishment potential balance

membrane potential

(Q013) Which of the following is a cell type in humans that uses voltage-gated ion channels? muscle cells skin cells liver cells gut epithelial cells

muscle cells

(Q011) Ion channels contain a selectivity filter that binds with extreme sensitivity to their specific ion, akin to an enzyme forming a specific binding site for a substrate. selects for ions based on size and charge due to the width of the channel and charge of amino acids lining the channel. selects for size of ions based on interactions with the ion transport protein. selects for positively charged ions by virtue of the negatively charged amino acids lining the pore, but allows similar ions through, like Na+ and K+.

selects for ions based on size and charge due to the width of the channel and charge of amino acids lining the channel.

(Q004) Cells, compared with the extracellular fluid are electrically neutral. slightly positively charged. extremely positively charged. slightly negatively charged.

slightly negatively charged.

(Q020) What is the molecular target of the antidepressant Prozac? the symport that drives reuptake of serotonin the Na+ channels that activate the neuron the K+ channels that deactivate action potentials the serotonin receptor, a transmitter-gated ion channel

the symport that drives reuptake of serotonin