Question 1

Which of the following best describes the main function of the hydrophobic interior of the phospholipid bilayer in biological membranes?

Accepted Answer

It acts as a permeability barrier, blocking the passage of polar molecules and ions.

Question 2

Which experimental finding most directly led Gorter and Grendel to propose the lipid bilayer model of the plasma membrane?

Accepted Answer

The area of the lipid film extracted from erythrocytes was about twice the estimated surface area of the cells.

Question 3

Which of the following is a key feature of the fluid mosaic model of membrane structure proposed by Singer and Nicolson?

Accepted Answer

Proteins are embedded within or attached to a fluid lipid bilayer, allowing lateral movement.

Question 4

A mutation in the gene encoding spectrin leads to hereditary spherocytosis. Which cellular structure is most directly affected by this mutation?

Accepted Answer

The plasma membrane of erythrocytes

Question 5

Which of the following statements about membrane asymmetry is CORRECT?

Accepted Answer

Glycolipids are typically found on the outer monolayer, with carbohydrate groups protruding from the cell surface.

Question 6

Which of the following best explains why cholesterol acts as a 'fluidity buffer' in animal cell membranes?

Accepted Answer

Cholesterol decreases membrane fluidity at high temperatures and increases it at low temperatures.

Question 7

A researcher uses thin-layer chromatography (TLC) to analyze the lipid composition of a cell membrane. Which property of the lipids is primarily responsible for their separation on the TLC plate?

Accepted Answer

Degree of polarity

Question 8

Which of the following changes would most likely increase the fluidity of a biological membrane at a given temperature?

Accepted Answer

Increasing the proportion of unsaturated fatty acids

Question 9

Which class of membrane proteins is most likely to be extracted from the membrane by changing the pH or ionic strength of the solution?

Accepted Answer

Peripheral membrane proteins

Question 10

A patient with Tay-Sachs disease has a deficiency in the enzyme hexosaminidase A. Which of the following best describes the consequence of this deficiency?

Accepted Answer

Accumulation of gangliosides in nerve cells, leading to impaired brain function

Question 11

Which of the following best describes the effect of cis double bonds in unsaturated fatty acids on membrane structure?

Accepted Answer

They introduce kinks that prevent tight packing, increasing membrane fluidity.

Question 12

Which of the following experimental techniques would be most appropriate to determine the lateral mobility of membrane proteins in living cells?

Accepted Answer

Fluorescence recovery after photobleaching (FRAP)

Question 13

Which of the following is a real-life example of membrane protein function in signal transduction?

Accepted Answer

Insulin binding to its receptor on muscle and liver cells, triggering glucose uptake

Question 14

Which of the following statements about the protein/lipid ratio in biological membranes is TRUE?

Accepted Answer

The protein/lipid ratio varies depending on the membrane's function and source.

Question 15

Which of the following best explains why trans fats are considered unhealthy compared to cis unsaturated fats?

Accepted Answer

Trans fats pack more tightly in membranes, increasing transition temperature and decreasing fluidity, similar to saturated fats.

Question 16

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

Accepted Answer

Serving as markers for cell-cell recognition and adhesion

Question 17

A scientist is studying a membrane protein that spans the lipid bilayer seven times and functions as a light-activated proton pump. Which protein is being described?

Accepted Answer

Bacteriorhodopsin

Question 18

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

Accepted Answer

They catalyze the flip-flop (transverse diffusion) of specific phospholipids between membrane monolayers.

Question 19

Which of the following statements about the permeability of biological membranes is CORRECT?

Accepted Answer

The presence of sterols decreases the permeability of membranes to ions and small polar molecules.

Question 20

Which of the following best describes homeoviscous adaptation in poikilothermic organisms?

Accepted Answer

The ability to regulate membrane fluidity by altering lipid composition in response to temperature changes

Membrane Structure and Function: The Fluid Mosaic Model and Its Components

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