Question 1

Which of the following best describes the selectivity of ion channels in the plasma membrane?

Accepted Answer

Ion channels are selective due to binding sites involving amino acid side chains and a size filter.

Question 2

A mutation in the CFTR protein leads to cystic fibrosis. What is the primary function of the CFTR protein in healthy lung cells?

Accepted Answer

It maintains the proper Cl$$^-$$ concentration by acting as a chloride ion channel.

Question 3

Which type of channel protein is most likely to facilitate the rapid passage of water molecules across the cell membrane?

Accepted Answer

Aquaporins

Question 4

Porins are found in the outer membranes of bacteria and mitochondria. What structural feature allows porins to transport a variety of hydrophilic solutes?

Accepted Answer

A water-filled pore lined with polar side chains inside a $$\beta$$ barrel structure

Question 5

Which of the following is NOT a type of gated ion channel?

Accepted Answer

Aquaporin-gated channel

Question 6

A cell needs to import glucose from the intestine even when the concentration of glucose is higher inside the cell than outside. Which transport mechanism is used?

Accepted Answer

Indirect active transport via the Na$$^+/$$glucose symporter

Question 7

Which equation correctly calculates the free energy change ($$\Delta G) $$for the inward transport of an uncharged solute S?

Accepted Answer

$$\Delta G = RT \ln \frac{[S]_{inside}}{[S]_{outside}}$$

Question 8

A cell has [Na$$^+$$]$$_{out} = 150 mM$$, [Na$$^+$$]$$_{in} = 5 mM$$, and a membrane potential $$V_m = -70 mV. $$What is the correct formula to calculate the free energy change for Na$$^+$$ import?

Accepted Answer

$$\Delta G = RT \ln \frac{[Na^+]_{in}}{[Na^+]_{out}} + zF V_m$$

Question 9

Which of the following statements about the Na$$^+/K$^+$$ ATPase pump is TRUE?

Accepted Answer

It is a P-type ATPase that is reversibly phosphorylated during its catalytic cycle.

Question 10

Which of the following is a medically significant function of ABC-type ATPases?

Accepted Answer

They pump antibiotics or drugs out of cells, contributing to multidrug resistance.

Question 11

Bacteriorhodopsin uses light energy to transport protons. What is the immediate result of this transport in halobacteria?

Accepted Answer

Creation of an electrochemical proton gradient across the membrane

Question 12

Which of the following best explains why aquaporins are necessary in erythrocytes and kidney cells?

Accepted Answer

Water movement across the membrane is much faster than expected due to aquaporins facilitating rapid passage.

Question 13

Which of the following is a key difference between direct and indirect active transport?

Accepted Answer

Direct active transport uses ATP hydrolysis directly, while indirect active transport uses the energy of diffusion of another solute.

Question 14

A patient’s tumor cells are found to be resistant to chemotherapy drugs. Which protein is most likely overexpressed in these cells?

Accepted Answer

MDR (multidrug resistance) ABC transporter

Question 15

Which of the following is TRUE about the conformational states of the Na$$^+/K$^+$$ pump?

Accepted Answer

E$$_1$$ conformation is open to the inside and has high affinity for Na$$^+$$ ions.

Question 16

Which of the following ATPase types is primarily responsible for acidifying lysosomes and vacuoles?

Accepted Answer

V-type ATPases

Question 17

A scientist wants to determine the energy required for the inward transport of lactose in a bacterium. If the internal concentration is 10 mM and the external is 0.20 mM, which calculation should be performed?

Accepted Answer

$$\Delta G = RT \ln \frac{10}{0.20}$$

Question 18

Which of the following best describes the structure of aquaporins?

Accepted Answer

Tetrameric integral membrane proteins with four central channels lined with hydrophilic side chains

Membrane Transport Proteins: Channels, Porins, Aquaporins, and Active Transport

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