GCD 3033 Chapter 12

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? A. glucose B. water C. glycerol D. ethanol

glucose

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

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

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

Ethanol

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

False

Aquaporin channels are found in the plasma membrane, allowing the rapid passage of water molecules and small ions in and out of cells.

False

Facilitated diffusion can be described as the favorable movement of one solute down its concentration gradient being coupled with the unfavorable movement of a second solute up its concentration gradient.

False

Gap junctions are large pores that connect the cytosol to the extracellular space.

False

The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content.

False

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

False

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

False

Which molecule is more likely to diffuse through the lipid bilayer? Glycerol or RNA...

Glycerol

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?

Cl-

Which of the following statements is true? A. Amoebae have transporter proteins that actively pump water molecules from the cytoplasm to the cell exterior. B. Bacteria and animal cells rely on the Na+-K+ pump in the plasma membrane to prevent lysis resulting from osmotic imbalances. C. The Na+-K+ pump allows animal cells to thrive under conditions of very low ionic strength. D. The Na+-K+ pump helps to keep both Na+ and Cl- ions out of the cell.

The Na+-K+ pump helps to keep both Na+ and Cl- ions out of the cell.

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? A. The temperature is 37°C. B. The plasma membrane is primarily permeable to Na+. C. At rest, the interior of the cell is more negatively charged than the exterior. D. K+ is the principal positive ion in the cell.

The plasma membrane is primarily permeable to Na+.

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

True

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

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 transport

A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethanol in the process: C6H12O6 + 2ADP + 2Pi + H+ → 2CO2 + 2CH3CH2OH + 2ATP + 2H2O Unfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following could account for the yeast cell's demise? A. toxic buildup of carbon dioxide inside the cell B. toxic buildup of ethanol inside the cell C. diffusion of ATP out of the cell D. inability to import sugar into the cell

inability to import sugar into the cell

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

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 & some open completely

Transporters, in contrast to channels, work by ________________.

specific binding to solutes

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

stress-gated

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

_______ ion channels respond to changes in membrane potential.

voltage-gated

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

voltage-gated Ca2+ channels

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

The Nernst equation can be used to calculate the membrane potential based on the ratio of the outer and inner ion concentration. In a resting cell, membrane potential is calculated taking only K+ ions into account. What is V when Co = 15 mM and Ci = 106 mM?

-52.7 mV

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

False

For an uncharged molecule, the direction of passive transport across a membrane is determined solely by its ___A___ gradient. On the other hand, for a charged molecule, the ___B___ must also be considered. The net driving force for a charged molecule across a membrane therefore has two components and is referred to as the ___C___ gradient. Active transport allows the movement of solutes against this gradient. The transporter proteins called ___D___ transporters use the movement of one solute down its gradient to provide the energy to drive the uphill transport of a second gradient. When this transporter moves both ions in the same direction across the membrane, it is considered a(n) ___E___; if the ions move in opposite directions, the transporter is considered a(n) ___F___.

A - concentration B - membrane potential C - electrochemical D - coupled E - symport F - antiport

The action potential is a wave of ___A___ that spreads rapidly along the neuronal plasma membrane. This wave is triggered by a local change in the membrane potential to a value that is ___B___ negative than the resting membrane potential. The action potential is propagated by the opening of ___C___-gated channels. During an action potential, the membrane potential changes from ___D___ to___E___. The action potential travels along the neuron's ___F___ to the nerve terminals. Neurons chiefly receive signals at their highly branched ___G___.

A - depolarization B - less C - voltage D - negative E - positive F - axon G - dendrites

A molecule moves down its concentration gradient by ___A___ transport, but requires ___B___ transport to move up its concentration gradient. Transporter proteins and ion channels function in membrane transport by providing a ___C___ pathway through the membrane for specific polar solutes or inorganic ions. ___D___ are highly selective in the solutes they transport, binding the solute at a specific site and changing its conformation so as to transport the solute across the membrane. On the other hand, ___E___ discriminate between solutes mainly on the basis of size and electrical charge.

A - passive B - active C - hydrophilic D - transporter proteins E - ion channels

Neurons communicate with each other through specialized sites called ___A___. Many neurotransmitter receptors are ligand-gated ion channels that open transiently in the ___B___ cell membrane in response to neurotransmitters released by the ___C___ cell. Ligand-gated ion channels in nerve cell membranes convert ___D___ signals into ___E___ ones. Neurotransmitter release is stimulated by the opening of voltage-gated ___F___ in the nerve terminal membrane.

A - synapses B - postsynaptic C - presynaptic D - chemical E - electrical F - Ca++ channels

You have generated antibodies that recognize the extracellular domain of the Ca2+ pump. Adding these antibodies to animal cells blocks the active transport of Ca2+ from the cytosol into the extracellular environment. What do you expect to observe with respect to intracellular Ca2+?

Ca++ pumps in the ER membrane keep cystolic calcium levels low

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

Benzene

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

False

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?

H+

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

It opens more frequently in response to a given stimulus.

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?

K+ coupled

Which molecule is more likely to diffuse through the lipid bilayer? H2O or O2...

O2

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? A. The action potential will be smaller B. The action potential will be larger

The action potential will be lager

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? A. The action potential will be smaller B. The action potential will be larger

The action potential will be smaller

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

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

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

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

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

True

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

True

Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential? A. by closing Na+ channels B. by preventing the secretion of excitatory neurotransmitters C. by opening K+ channels D. by opening Cl- channels

by opening Cl- channels

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 negative

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