Ch. 12 quiz

The ion selectivity of a channel completely depends solely on the charge of the amino acids lining the pore inside the channel. true or false

False

Transporters are similar to channels, except that they are larger, allowing folded proteins as well as smaller organic molecules to pass through them. true or false

False

We can test the relative permeability of a phospholipid bilayer by using a synthetic membrane that does not contain any protein components. Some uncharged, polar molecules are found to diffuse freely across these membranes, to varying degrees. Which of the following has the lowest rate of diffusion across an artificial membrane? Glucose water glycerol ethanol

Glucose

Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is not one of the common ways to perform active transport? Na+ coupled K+ coupled ATP-drive light-driven

K+coupled

The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. What type of neurotransmitter is used at these neuromuscular junctions?

Acetylcholine

Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is the principal anion? HCO3- Cl- PO4(3-) OH-

Cl-

Transporters, in contrast to channels, work by ________________.

Specific binding to solutes

The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. Which type of gating mechanism do these cells use?

Stress-gated

CO2 and O2 are water-soluble molecules that diffuse freely across cell membranes. true or false

True

Cells expend energy in the form of ATP hydrolysis so as to maintain ion concentrations that differ from those found outside the cell. true or false

True

Most ion channels are gated, which allow them to open and close in response to a specific stimulus rather than allowing the constant, unregulated flow of ions. true or false

True

Which of the following is required for the secretion of neurotransmitters in response to an action potential? neurotransmitter receptors Na+-K+ pumps voltage-gated K+ channels voltage-gated Ca2+ channels

Voltage-gated Ca2+ channels

Studies on the squid giant axon were instrumental in our current understanding of how action potentials are generated. You decide to do an experiment on the squid giant axon yourself. You add NaCl to the extracellular fluid and effectively double the amount of extracellular Na+ cation. How does this affect the action potential?

action potential will be larger

Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called _____________.

active

Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential?

by opening Cl- channels

If Na+ channels are opened in a cell that was previously at rest, how will the resting membrane potential be affected?

it becomes more positive

Which of the following best describes the behavior of a gated channel? It stays open continuously when stimulated. It opens more frequently in response to a given stimulus. It opens more widely as the stimulus becomes stronger. It remains closed if unstimulated.

it opens more frequently in response to a given stimulus

Many receptors for neurotransmitters are _______ ion channels.

ligand gated

The acetylcholine receptor in skeletal muscle cells is a(n) _______ ion channel.

ligand-gated

Studies on the squid giant axon were instrumental in our current understanding of how action potentials are generated. You decide to do an experiment on the squid giant axon yourself. You remove the cytoplasm in an axon and replace it with an artificial cytoplasm that contains twice the normal concentration of K+ by adding KOAc, where OAc- is an anion that is impermeable to the membrane. In this way you double the internal concentration of K+ while maintaining the bulk electrical balance of the cytoplasmic solution. Will this make the resting potential of the membrane more or less negative?

more neg

Which molecule is more likely to diffuse through the lipid bilayer? H20 O2

o2

Ca2+ pumps in the plasma membrane and endoplasmic reticulum are important for _____________.

preventing Ca2+ from altering the activity of the molecules in the cytosol

Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold? Some channels remain closed and some open completely. All channels open completely. All channels open partly, to the same degree. All channels open partly, each to a different degree.

some channels remain closed and some open completely

_______ ion channels are found in the hair cells of the mammalian cochlea.

stress gated

Studies on the squid giant axon were instrumental in our current understanding of how action potentials are generated. You decide to do an experiment on the squid giant axon yourself. You replace half of the NaCl in the extracellular fluid with choline chloride. (Choline is a monovalent cation much larger than Na+. Note that the presence of choline will not impede the flow of Na+ through its channels.) How will this affect the action potential?

the action potential will be smaller

When using the Nernst equation to calculate membrane potential, we are making several assumptions about conditions in the cell. Which of the following is not a good assumption? The temperature is 37°C. The plasma membrane is primarily permeable to Na+. At rest, the interior of the cell is more negatively charged than the exterior. K+ is the principal positive ion in the cell.

the plasma membrane is primarily permeable to Na+

The Na+-K+ ATPase is also known as the Na+-K+ pump. It is responsible for maintaining the high extracellular sodium ion concentration and the high intracellular potassium ion concentration. What happens immediately after the pump hydrolyzes ATP?

the pump is phosphorylated

K+ leak channels are found in the plasma membrane. These channels open and close in an unregulated, random fashion. What do they accomplish in a resting cell?

they keep the electrochemical gradient for K+ at zero

Neurotransmitters are small molecules released into the synaptic cleft after the fusion of synaptic vesicles with the presynaptic membrane. true or false

true

The electrochemical gradient for K+ across the plasma membrane is small. Therefore, any movement of K+ from the inside to the outside of the cell is driven solely by its concentration gradient. true or false

true

Transporters undergo transitions between different conformations, depending on whether the substrate-binding pocket is empty or occupied. true or false

true

Voltage-gated Na+ channels become automatically inactivated shortly after opening, which ensures that the action potential cannot move backward along the axon. true or false

true

_______ ion channels respond to changes in membrane potential.

voltage -gated

The net negative charge on the cytosolic side of the membrane enhances the rate of glucose import into the cell by a uniporter. true or false

false

Voltage-gated K+ channels also open immediately in response to local depolarization, reducing the magnitude of the action potential. true or false

false

Which molecule is more likely to diffuse through the lipid bilayer? Cl- ethanol

ethanol

Action potentials are usually mediated by voltage-gated Ca2+ channels. true or false

false

Which molecule is more likely to diffuse through the lipid bilayer? Amino acids benzene

Benzene

Ion channels are classified as membrane transport proteins. Channels discriminate by size and charge. In addition to Na+, which one of the following ions would you expect to be able to freely diffuse through a Na+ channel? Mg2+ H+ K+ Cl-

H+