Question 1

Which of the following best describes the main function of the plasma membrane in eukaryotic cells?

Accepted Answer

It acts as a selective barrier, regulating the movement of substances in and out of the cell.

Question 2

Which experimental evidence first suggested that the cell membrane is composed of a lipid bilayer?

Accepted Answer

Gorter and Grendel's extraction of lipids from red blood cells and measurement of the surface area of the lipid film.

Question 3

Which of the following statements about membrane fluidity is CORRECT?

Accepted Answer

Sterols act as fluidity buffers, decreasing fluidity at high temperatures and preventing solidification at low temperatures.

Question 4

A mutation in a plant causes a deficiency in the enzyme desaturase. Which of the following is the most likely consequence for the plant's cell membranes at low temperatures?

Accepted Answer

The membranes will become less fluid and may solidify, impairing function.

Question 5

Which of the following best explains why unsaturated fatty acids increase membrane fluidity?

Accepted Answer

Their cis double bonds introduce kinks, preventing tight packing of phospholipids.

Question 6

Which of the following is a function of glycoproteins in the plasma membrane?

Accepted Answer

Facilitating cell-cell recognition and immune responses.

Question 7

A researcher uses SDS-PAGE to analyze membrane proteins. What is the primary effect of SDS on the proteins?

Accepted Answer

It coats proteins with negative charges and disrupts protein-protein and protein-lipid interactions.

Question 8

Which of the following best describes the difference between integral and peripheral membrane proteins?

Accepted Answer

Integral proteins span the lipid bilayer with hydrophobic regions, while peripheral proteins are bound to the membrane surface by weak interactions.

Question 9

Which of the following is a key feature of the fluid mosaic model of membrane structure?

Accepted Answer

The membrane consists of a fluid lipid bilayer with a mosaic of proteins attached or embedded.

Question 10

Which of the following experimental techniques would be most appropriate to determine the number and location of transmembrane segments in a membrane protein?

Accepted Answer

Hydropathy plot analysis

Question 11

Which of the following statements about membrane asymmetry is TRUE?

Accepted Answer

Membrane asymmetry is established during synthesis and is maintained throughout the life of the membrane.

Question 12

Which of the following best describes the role of lipid rafts in the plasma membrane?

Accepted Answer

They are dynamic microdomains rich in cholesterol and glycosphingolipids that organize membrane proteins and facilitate signal transduction.

Question 13

Which of the following cell junctions allows for the rapid passage of electrical signals between adjacent animal cells?

Accepted Answer

Gap junctions

Question 14

A patient has a genetic defect in cadherin proteins. Which of the following cellular processes is most likely to be affected?

Accepted Answer

Cell-to-cell adhesion in tissues

Question 15

Which of the following statements about the permeability of the lipid bilayer is CORRECT?

Accepted Answer

Small nonpolar molecules can diffuse directly across the bilayer, while ions require specific transport proteins.

Question 16

Which of the following best explains why cholesterol decreases membrane permeability to small polar molecules?

Accepted Answer

Cholesterol fills spaces between phospholipid hydrocarbon chains, reducing gaps for polar molecules to pass through.

Question 17

Which of the following is a real-world application of lectin affinity chromatography?

Accepted Answer

Screening for potential cancer biomarkers by detecting specific glycoproteins

Question 18

A scientist is studying a membrane protein that is difficult to extract from the membrane. Which of the following is the most likely reason?

Accepted Answer

The protein is integral and has hydrophobic transmembrane segments.

Question 19

Which of the following best describes the process of fluorescence recovery after photobleaching (FRAP) in studying membrane dynamics?

Accepted Answer

It demonstrates lateral diffusion of membrane lipids and proteins by monitoring the recovery of fluorescence in a bleached area.

Question 20

Which of the following equations correctly represents the relationship between the transition temperature ($$T_m) of a $$membrane and the characteristics of its fatty acids?

Accepted Answer

$$T_m$$ increases with increasing chain length and degree of saturation of fatty acids.

CH 7 - Membranes – Structure, Function, and Chemistry

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