Question 1

Which experimental evidence led Gorter and Grendel to propose the lipid bilayer model for cell membranes?

Accepted Answer

They observed that the surface area of the lipid film was twice the surface area of the red blood cells.

Question 2

A membrane is composed of phospholipids with unsaturated fatty acid tails. Which effect will this have on membrane fluidity, and why?

Accepted Answer

Membrane fluidity will increase because unsaturated fatty acids prevent tight packing.

Question 3

Which of the following best describes the fluid mosaic model of membrane structure?

Accepted Answer

A bilayer of lipids with proteins embedded within and on the surface, both components able to move laterally.

Question 4

You collect 1000 red blood cells with a combined surface area of 8 cm$^2$. After dissolving their plasma membranes in benzene and layering the phospholipids on water, what surface area would you expect for the layered phospholipids?

Accepted Answer

$16\ 	ext{cm}^2$

Question 5

Which factor would most likely increase the transition temperature ($T_m$) of a membrane?

Accepted Answer

Increasing the proportion of saturated fatty acids.

Question 6

Why is transverse diffusion (flip-flop) of lipids more frequent in living biological membranes than in artificial bilayers?

Accepted Answer

Cells contain a protein (flippase) that catalyzes the transverse diffusion of lipids.

Question 7

Which of the following is a major function of cell membranes as illustrated in the study materials?

Accepted Answer

Boundary and permeability barrier

Question 8

Which class of membrane proteins is embedded in the lipid bilayer due to hydrophobic regions?

Accepted Answer

Integral membrane proteins

Question 9

What is the main sterol found in animal cell membranes, and what is its primary function?

Accepted Answer

Cholesterol; stabilizes and maintains membrane structure

Question 10

Which process is used to measure the mobility of lipids in membranes, and what does it involve?

Accepted Answer

FRAP; labeling lipids with a fluorescent dye and observing recovery after photobleaching

Question 11

Which of the following statements about membrane asymmetry is correct?

Accepted Answer

Membrane asymmetry is established during membrane synthesis and maintained over time.

Question 12

Which of the following best explains why cholesterol reduces membrane fluidity at higher temperatures but prevents gel formation at lower temperatures?

Accepted Answer

Cholesterol's rigid structure restricts movement at high temperatures and disrupts packing at low temperatures.

Question 13

Which of the following membrane proteins displays clear quaternary structure?

Accepted Answer

Multi-subunit protein

Question 14

Which type of glycosylation involves the linkage of a carbohydrate chain to the nitrogen atom of an amino group of an asparagine residue?

Accepted Answer

N-linked glycosylation

Question 15

Which of the following sugars is NOT commonly found in glycoproteins?

Accepted Answer

Glucose

Question 16

A membrane protein is found to be glycosylated. Where did this glycosylation most likely occur?

Accepted Answer

Endoplasmic reticulum and Golgi apparatus

Question 17

Which of the following best describes the movement of lipids within a membrane?

Accepted Answer

Lipids move rapidly and randomly within their monolayer by rotation and lateral diffusion.

Question 18

Which of the following is a consequence of increasing the length of the hydrocarbon tail in membrane phospholipids?

Accepted Answer

Transition temperature ($T_m$) increases.

Question 19

Which of the following is a real-world application of the fluid mosaic model in medicine?

Accepted Answer

Explaining how viruses fuse with host cell membranes during infection.

Membranes: Structure, Function, and Chemistry – Study Notes

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