Question 1

Which of the following best explains why amphipathic molecules with a larger head group than acyl side chain(s) tend to form micelles rather than bilayers in aqueous solution?

Accepted Answer

Because the wedge-shaped structure allows the hydrophobic tails to avoid water more efficiently in a spherical arrangement.

Question 2

Which of the following statements about biological membranes is FALSE?

Accepted Answer

All biological membranes have the same composition.

Question 3

A protein that spans the membrane once, with a single hydrophobic sequence, is best classified as:

Accepted Answer

Bitopic

Question 4

Which of the following best describes the function of flippases in the plasma membrane?

Accepted Answer

They catalyze the translocation of phosphatidylethanolamine (PE) and phosphatidylserine (PS) from the extracellular to the cytoplasmic leaflet, using ATP.

Question 5

Which of the following equations correctly describes the free-energy change for the transport of an uncharged solute from concentration $$C_1 to$$ $$C_2$$ across a membrane?

Accepted Answer

$$\Delta G_t = RT \ln\left(\frac{C_2}{C_1}\right)$$

Question 6

Which of the following is a characteristic of ion channels but NOT of transporters?

Accepted Answer

They are not saturable with their ion substrate.

Question 7

A mutation in the ABCB1 gene would most likely affect which cellular process?

Accepted Answer

The removal of toxic compounds and multidrug resistance in tumor cells.

Question 8

Which of the following best explains why cholesterol can both increase and decrease membrane fluidity depending on the fatty acid composition?

Accepted Answer

Cholesterol interacts with unsaturated fatty acyl chains to compact them, but makes the bilayer more fluid when associated with saturated chains.

Question 9

Which of the following best describes the mechanism of the Na$$^+/K$^+$$ ATPase?

Accepted Answer

It couples the phosphorylation and dephosphorylation of a critical Asp residue to the movement of Na$$^+$$ and K$$^+$$ against their electrochemical gradients.

Question 10

A patient with cystic fibrosis has a mutation in which type of membrane protein?

Accepted Answer

An ABC transporter functioning as a Cl$$^-$$ channel (CFTR).

Question 11

Which of the following statements about the fluid mosaic model of membranes is correct?

Accepted Answer

Individual lipid and protein units can move laterally within the membrane, allowing for dynamic changes in membrane structure.

Question 12

Which of the following best describes the role of caveolin in the plasma membrane?

Accepted Answer

It binds to cholesterol-rich regions and induces inward curvature to form caveolae.

Question 13

Which of the following is the correct equation for the free-energy change for the transport of an ion across a membrane?

Accepted Answer

$$\Delta G_t = RT \ln\left(\frac{C_2}{C_1}\right) + ZF \Delta \psi$$

Question 14

Which of the following best describes the function of aquaporins?

Accepted Answer

They form hydrophilic transmembrane channels that allow rapid passage of water but not protons.

Question 15

Which of the following is true regarding the movement of phospholipids in biological membranes?

Accepted Answer

Lateral diffusion within a leaflet is rapid, while transbilayer (flip-flop) diffusion is much slower and often requires catalysis.

Question 16

Which of the following best describes the function of GLUT1 in erythrocytes?

Accepted Answer

It mediates passive transport of glucose into the cell, following Michaelis-Menten-like kinetics.

Question 17

Which of the following is a consequence of the positive-inside rule for membrane proteins?

Accepted Answer

Positively charged Lys and Arg residues are more commonly found on the cytoplasmic face of membrane proteins.

Question 18

Which of the following best describes the difference between primary and secondary active transport?

Accepted Answer

Primary active transport uses energy directly from ATP hydrolysis, while secondary active transport couples the uphill movement of one solute to the downhill movement of another.

Ch 11: Biological Membranes and Transport: Structure, Dynamics, and Function

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