Exam 12: Transport Across Cell Membranes

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?

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?

What chemical principles explain the observation that a protein-free lipid bilayer is a billion times more permeable to water than to a sodium ion?

Which of the following statements about resting membrane potential is FALSE?

Which of the following is required for the secretion of neurotransmitters in response to an action potential?

Transporters, in contrast to channels, work by

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 statements about the patch-clamp method is FALSE?

Order and describe all the molecular events required for the propagation of an action potential.Is propagation along the axon bidirectional? Why or why not?

The Aeroschmidt weed contains an ATP-driven ion pump in its vacuolar membrane that pumps potentially toxic heavy metal ions such as Zn²⁺ and Pb²⁺ into the vacuole.The pump protein cycles through a phosphorylated and an unphosphorylated state and works in a similar way to the Na⁺-K⁺ pump of animal cells.To study its action, you incorporate the unphosphorylated form of the protein into phospholipid vesicles containing K⁺ in their interiors.(You ensure that all of the protein molecules are oriented such that their cytosolic domains face the outside of your vesicles.) When you add Zn²⁺ and ATP to the solution outside such vesicles, you find that Zn²⁺ is pumped into the vesicle lumen.You then expose vesicles containing the pump protein to the solutes shown in Table 12-28. A B C D E F Outside + ATP + ATP ATP ATP Inside Table 12-28 You then determine the amount of phosphorylated and unphosphorylated ATP-driven ion pump protein in each sample.Your results are summarized in Table 12-28A, where a minus sign indicates an absence of a type of protein and a plus sign indicates its presence. A B C D E F Phosphorylated + - - - - ++ protein present Unphosphorylated ++ ++ ++ ++ ++ - protein present Table 12-28A You treat vesicles as in lane F, but before determining the phosphorylation state of the protein, you wash away the outside buffer and replace it with a buffer containing only Zn²⁺.What do you expect to happen in this sample, and what are the results you expect to observe with respect to phosphorylation and movement of K⁺?

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

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? Why?

The flow of ions through a gated channel can be studied using a method called "patch-clamp recording." A.How is a detached patch-clamp experiment set up, and what exactly does it mean to "clamp" an ion channel? B.How is it possible to collect the recordings shown in Figures Q12-16A and Q12-16B from a single ion channel? (A) (B) Figure 12-16

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?

Ion channels are classified as membrane transport proteins.They discriminate between ions based on 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? Explain your answer.

Which of the following statements is TRUE?

Cells make use of H⁺ electrochemical gradients in many ways.Which of the following proton transporters is used to regulate pH in animal cells?

Because the Na+/K+ pump moves these ions at the same rate in opposing directions across the plasma membrane, it creates a net balance of charges on each side of the membrane .Given this fact, explain how cells generate a membrane potential across the plasma membrane and suggest the consequences for cell functions if this capacity were handicapped.

Which of the following statements best reflects the nature of synaptic plasticity?

Some cells express aquaporin proteins-they are channel proteins that facilitate the flow of water molecules through the plasma membrane.What regulates the rate and direction of water diffusion across the membrane?