Question 1

Which of the following best explains why cholesterol is abundant in the plasma membrane but virtually absent in mitochondrial membranes?

Accepted Answer

Cholesterol modulates membrane fluidity and permeability, functions that are critical for the plasma membrane but not for mitochondrial membranes.

Question 2

Which of the following statements about lipid rafts is CORRECT?

Accepted Answer

Lipid rafts are enriched in glycosphingolipids and cholesterol, and they help segregate specific proteins within the membrane.

Question 3

A protein with several amphipathic helices inserted into one leaflet of the bilayer can induce membrane curvature. What is the primary mechanism for this effect?

Accepted Answer

The helices crowd the lipids in one leaflet, forcing the membrane to bend.

Question 4

Which of the following best describes the difference between simple diffusion and facilitated diffusion across biological membranes?

Accepted Answer

Facilitated diffusion is saturable and specific for certain molecules, while simple diffusion is not.

Question 5

The free energy change ($$\Delta G) $$for the movement of a charged molecule across a membrane is given by which equation?

Accepted Answer

$$\Delta G = RT \ln \frac{[C_2$]}{[C_1$]} + ZF\Delta \psi$$

Question 6

Which of the following is a characteristic of P-type ATPases such as the Na+/K+ ATPase?

Accepted Answer

They use ATP hydrolysis to drive the active transport of ions against their gradients.

Question 7

Which of the following best describes the role of caveolin in biological membranes?

Accepted Answer

Caveolin is an integral membrane protein that induces membrane curvature by forming dimers and anchoring to the membrane via acyl groups.

Question 8

Which of the following is TRUE regarding the distribution of phospholipids in the erythrocyte membrane?

Accepted Answer

Phosphatidylethanolamine is more abundant in the inner monolayer than the outer monolayer.

Question 9

Which of the following best explains why galactolipids are abundant in plant chloroplasts but almost absent in animal cells?

Accepted Answer

Galactolipids are required for photosynthetic membrane structure and function, which is unique to chloroplasts.

Question 10

Which of the following is a function of GPI-anchored proteins?

Accepted Answer

They are anchored to the outer leaflet of the plasma membrane via a glycosylphosphatidylinositol anchor.

Question 11

Which of the following best describes the effect of a protein with a high density of positive charge on its concave surface interacting with a membrane?

Accepted Answer

It interacts with negatively charged phospholipid head groups, favoring curvature of the bilayer.

Question 12

Which of the following is a distinguishing feature of sphingolipids compared to glycerophospholipids?

Accepted Answer

Sphingolipids contain a sphingosine backbone and can have complex oligosaccharide head groups.

Question 13

Which of the following best describes the process of catalyzed transbilayer ('flip-flop') diffusion in membranes?

Accepted Answer

It is catalyzed by enzymes such as flippases and requires energy input (ATP).

Question 14

Which of the following is TRUE regarding the formation of vesicles from a lipid bilayer?

Accepted Answer

Vesicles form when a bilayer curves to enclose an aqueous cavity, with the hydrophilic heads facing the aqueous interior and exterior.

Question 15

Which of the following best explains the role of SNARE proteins in membrane fusion?

Accepted Answer

SNARE proteins zip together, causing curvature and lateral tension that favor hemifusion and ultimately complete fusion of membranes.

Question 16

Which of the following is a correct statement about the asymmetry of biological membranes?

Accepted Answer

Carbohydrates are found only on the extracellular side of the plasma membrane.

Membranes, Membrane Proteins, and Transport Mechanisms

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