Question 1

What is the expected effect on salt accumulation in the plant vacuole of a mutation in the plant vacuolar ATPase that decreases the H⁺ concentration in the vacuole?

Accepted Answer

The vacuolar ATPase pumps H⁺ ions into the vacuole, creating a proton gradient that drives the secondary transport of other ions, such as Na⁺, into the vacuole for storage or detoxification. A decrease in H⁺ concentration in the vacuole due to a mutation in the ATPase would weaken this gradient, thereby reducing the energy available for Na⁺ transport into the vacuole, leading to decreased Na⁺ accumulation.

Question 2

Propose a rationale for why the import of sucrose into the plant vacuole is coupled to the export of H⁺ ion into the plant cytosol.

Accepted Answer

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Question 3

Transepithelial glucose transport uses a symporter to transport glucose up a concentration gradient by:

Accepted Answer

Transepithelial glucose transport uses a symporter that couples glucose transport to Na⁺ movement. Glucose and Na⁺ are transported across the epithelium simultaneously, with Na⁺ moving down its electrochemical gradient, driving glucose against its concentration gradient. This process is known as secondary active transport.

Question 4

What is the basic structural organization of an ABC superfamily transport protein?

Accepted Answer

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Question 5

Why are nongated channels important in the generation of a negative electric potential (voltage)of 50-70 mV inside the cell with respect to the outside?

Accepted Answer

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Question 6

The ΔG calculation for the two-Na⁺/one-glucose symporter includes which of the following terms?

Accepted Answer

The ΔG calculation for the two-Na⁺/one-glucose symporter includes all three terms: RT ln [glucoseᵢn]/[glucoseₒᵤt], 2RT ln [Na⁺ᵢn]/[Na⁺ₒᵤt], and 2FE (the electrostatic potential energy term). RT ln [glucoseᵢn]/[glucoseₒᵤt] accounts for the concentration gradient of glucose across the membrane, while 2RT ln [Na⁺ᵢn]/[Na⁺ₒᵤt] accounts for the concentration gradient of Na⁺ across the membrane. 2FE accounts for the energy required to move Na⁺ ions against their electrostatic potential. Thus, all three terms are needed to fully account for the ΔG of this symporter.

Question 7

Which of the following is true about cystic fibrosis?

Accepted Answer

Patients with the most common CFTR mutation, ΔF508, produce a mutated CFTR protein that is not properly transported to the membrane, leading to a lack of function. Choice A is incorrect because the normal CFTR channel protein is an ATP-gated chloride channel, not a uniporter. Choice B is also incorrect because CFTR mutations typically result in a decreased ability to transport chloride ions, leading to dehydration of secretions in various organs. Choice C is incorrect because there are several treatments for CF that target the CFTR receptor, such as CFTR modulators that improve the function of the mutated protein.

Question 8

Explain why ATP-powered proton pumps cannot by themselves acidify the lumen of the lysosome.

Accepted Answer

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Question 9

The resting membrane potential in animal cells depends largely on nongated _____ channels.

Accepted Answer

The rest membrane potential in animal cells depends largely on nongated K+ channels. This is because the concentration of K+ ions is typically higher inside the cell than outside, and the membrane is more permeable to K+ ions than to other ions such as Na+. As a result, K+ ions diffuse out of the cell more readily than Na+ ions diffuse into the cell, causing an overall negative charge inside the cell relative to the outside.

Question 10

What evidence suggests that all of the P-class ion pumps evolved from a common ancestor even though they now transport different ions?

Accepted Answer

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Question 11

The many pumps present in the membrane have interconnected and important functions.Which of the following functions is NOT correct?

Accepted Answer

P-class pumps are involved in maintaining the cytosolic levels of ions, but they are not involved in keeping the cytosolic levels of potassium low. Rather, P-class pumps are responsible for maintaining the cytosolic levels of potassium at appropriate levels.

Question 12

Propose a rationale for why the import of amino acids or sugars into cells is typically coupled to Na⁺ ion import.

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Question 13

Calculate the ΔG for the movement of Na⁺ from inside a typical mammalian cell to outside.

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Question 14

A mutant channel protein is expressed in an oocyte.Compared to patch clamping experiments in oocytes expressing the normal channel,the length of downward deviations is diminished by half.This indicates:

Accepted Answer

The downward deviations in patch clamping experiments represent the flow of ions through an open channel. The fact that the length of the downward deviations is diminished by half with the mutant channel indicates that it does not stay open as long as the normal channel. Therefore, the best choice is B, which states that the mutant channel doesn't stay open as long.

Question 15

How does inhibition of the Na⁺/K⁺ ATPase increase the force of heart muscle contraction?

Accepted Answer

Inhibition of Na+/K+ ATPase leads to an increase in cytosolic Na+ levels. This increase in cytosolic Na+ maintains a high concentration of Na+ in the cell and reduces the electrochemical gradient for Na+ entry during the next action potential. This alteration of Na+ concentration leads to the decrease of the export of intracellular Ca2+ through the Na+/Ca2+ exchanger, increasing cytosolic Ca2+ and increasing the force of heart muscle contraction.

Question 16

Ion channels achieve selectivity in transport through all of the following mechanisms EXCEPT:

Accepted Answer

Ion channels achieve selectivity through mechanisms such as divergent evolution from a single type of channel protein, low activation energy for selective passage of the dehydrated ion, and the use of P segments to form an ion selectivity filter. The concept of evolving from distinct and different parent proteins does not directly contribute to the selectivity in transport of ion channels.

Question 17

The movement of dietary glucose and sodium from the intestine into the bloodstream relies on which of the following transport mechanisms?

Accepted Answer

The movement of dietary glucose and sodium from the intestine into the bloodstream involves all listed mechanisms: sodium glucose symporters facilitate the co-transport of glucose and sodium across the cell membrane, transcellular transport describes the movement through the cell (entering one side and exiting the other), and sodium/potassium ATPase helps maintain the sodium gradient necessary for glucose transport.

Question 18

Describe in general terms how the muscle Ca²⁺ ATPase pumps Ca²⁺ ions from the cytosol into the sarcoplasmic reticulum (SR).

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Question 19

Describe the patch-clamping technique.Why do investigators often use frog oocytes in their patch-clamping investigations?

Accepted Answer

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Question 20

The magnitude of the membrane electrical potential is calculated by:

Accepted Answer

The Nernst equation is used to calculate the membrane potential (voltage) of a cell, based on the distribution of ions across the membrane and their individual equilibrium potentials. It takes into account the charges and concentrations of different ions, as well as temperature and the universal gas constant.

Quiz 10: Transmembrane Transport of Ions and Small Molecules