CH 12

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant outside a typical mammalian cell? (a) Na+ (b) K+ (c) Ca2+ (d) Cl-

(a) Na+

Which of the following channels would not be expected to generate a change in voltage by movement of its substrate across the membrane where it is found? (a) an aquaporin (b) a sodium channel (c) a calcium channel (d) a proton channel

(a) an aquaporin

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+? (a) Ca2+-pumps in vesicle membranes keep cytosolic calcium levels low. (b) Ca2+-pumps in the endoplasmic reticulum membrane keep cytosolic calcium levels low. (c) Ca2+-pumps in the Golgi apparatus keep cytosolic calcium levels low. (d) Ca2+ concentrations in the cytosol increase at a steady rate.

(b) Ca2+-pumps in the endoplasmic reticulum membrane keep cytosoliccalcium levels low.

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 (a) Na+-coupled (b) K+-coupled (c) ATP-driven (d) light-driven

(b) K+-coupled

Which of the following occur without coupling transport of the solute to the movement of a second solute? (a) import of glucose into gut epithelial cells (b) export of Ca2+ from the cytosol (c) export of H+from animal cells for pH regulation (d) the export of Na+ from cells to maintain resting membrane potential

(b) export of Ca2+ from the cytosol

T/F: Aquaporin channels are found in the plasma membrane, and allow the rapid passage of water molecules and small ions in and out of cells

F

T/F: Cytosolic Ca2+ concentration is kept low by the use of chelators such as EDTA.

F

T/F: The net negative charge on the cytosolic side of the membrane enhances the rate of glucose import into the cell by a uniporter

F

T/F: The primary mechanism by which Ca2+ acts as a signaling molecule is by increasing the net charge in the cytosol.

F

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? A) HCO3- B) Cl- C) PO43- D) OH-

B) Cl-

T/F: The extracellular concentration of Ca2+ is approximately 10^4-fold higher than the concentration of Ca2+ in the cytosol.

T

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

T

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

T

_________ ion channels in the mimosa plant propagate the leaf-closing response.

Voltage-gated

_________ ion channels respond to changes in membrane potential.

Voltage-gated

Transporters, in contrast to channels, work by ________________. a. specific recognition of transport substrates b. a gating mechanism c. filtering solutes by charge d. filtering solutes by size

a. specific recognition of transport substrates

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

passive active hydrophilic transporter proteins ion channels

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? (a) Na+is bound (b) ADP is bound (c) the pump is phosphorylated (d) the pump changes conformation

(c) the pump is phosphorylated

Cells make use of H+ electrochemical gradients in many ways. Which of the following proton transporters is used to regulate pH in animal cells? (a) light-driven pump (b) H+ATPase (c) H+symporter (d) Na+-H+exchanger

(d) Na+-H+exchanger

In a method called patch-clamping, a glass capillary can be converted into a microelectrode that measures the electrical currents across biological membranes.Which of the following is not true about the patch-clamp method? (a) The glass capillary adheres to a "patch" of membrane through the application of suction. (b) The aperture in the glass capillary used to make a microelectrode is about 1 µm in diameter. (c) If the experimental conditions are held constant, fluctuations in electrical currents across the patch of membrane are still observed. (d) Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli.

(d) Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli.

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

(d) by opening Cl-channels

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

D) inability to import sugar into the cell

Figure 1. illustrates changes in membrane potential during the formation of an action potential. What membrane characteristic or measurement used to study action potentials is indicated by the arrow? a. effect of a depolarizing stimulus b. resting membrane potential c. threshold potential d. action potential

c. threshold potential

For an uncharged molecule, the direction of passive transport across a membrane is determined solely by its __________________ gradient. On the other hand, for a charged molecule, the __________________ 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 __________________ gradient. Active transport allows the movement of solutes against this gradient. The transporter proteins called __________________ transporters use the movement of one solute down its gradient to provide the energy to drive the uphill transport of a second solute. When this transporter moves both ions in the same direction across the membrane, it is considered a(n) __________________; if the ions move in opposite directions, the transporter is considered a(n) __________________. antiport coupled membrane potential ATP hydrolysis electrochemical symport concentration light-driven uniport

concentration membrane potential electrochemical coupled symport antiport