$$T_m \propto \text{chain length} \times \text{saturation}$$

Question 1

Which of the following best describes the 'fluid mosaic model' of cell membranes?

Accepted Answer

A sea of phospholipids in which proteins float and move, creating a dynamic and diverse membrane

Question 2

Which membrane component is primarily responsible for the permeability barrier that separates the cell from its environment?

Accepted Answer

Phospholipid bilayer

Question 3

A scientist uses thin-layer chromatography (TLC) to analyze membrane lipids. Which principle allows TLC to separate lipids?

Accepted Answer

Lipids are separated based on their relative polarity and affinity for the polar silicic acid plate

Question 4

Which of the following statements about membrane asymmetry is correct?

Accepted Answer

Membrane asymmetry is established during membrane synthesis and is maintained because flip-flop movement is rare

Question 5

Which of the following would most likely increase the fluidity of a cell membrane at low temperatures?

Accepted Answer

Increasing the proportion of unsaturated fatty acids with cis double bonds

Question 6

A poikilothermic organism is exposed to a drop in environmental temperature. Which adaptation would help maintain membrane fluidity?

Accepted Answer

Increasing the degree of unsaturation in membrane fatty acids via desaturase enzymes

Question 7

Which equation best represents the relationship between transition temperature ($$T_m) $$and fatty acid chain length and saturation?

Accepted Answer

$$T_m \propto 	ext{chain length} 	imes 	ext{saturation}$$

Question 8

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

Accepted Answer

Cholesterol decreases fluidity at high temperatures and prevents gelling at low temperatures

Question 9

Which membrane protein type is most likely to be extracted by changing the pH or ionic strength of the solution?

Accepted Answer

Peripheral membrane proteins

Question 10

A hydropathy plot is used to analyze a membrane protein. What does a positive hydropathy index indicate?

Accepted Answer

A region of the protein likely to be hydrophobic and embedded in the lipid bilayer

Question 11

Which of the following is a real-world example of membrane glycoproteins playing a critical role in cell-cell recognition?

Accepted Answer

The ABO blood group system in humans

Question 12

Which experimental evidence supports the mobility of membrane proteins within the lipid bilayer?

Accepted Answer

Cell fusion experiments using fluorescently labeled antibodies (Frye and Edidin)

Question 13

Which of the following best describes the role of tight junctions in multicellular organisms?

Accepted Answer

They form seals that block the passage of fluids between cells

Question 14

Which of the following is true regarding the effect of trans fatty acids on membrane fluidity?

Accepted Answer

Trans fatty acids pack together like saturated fatty acids, decreasing membrane fluidity

Question 15

Which of the following best explains why most bacteria lack sterols in their membranes?

Accepted Answer

Bacteria use hopanoids instead, which serve a similar function to sterols

Question 16

Which of the following is a function of the glycocalyx in animal cells?

Accepted Answer

Providing cell-cell recognition and adhesion, protection, and creating permeability barriers

Question 17

Which of the following best describes the orientation of membrane proteins across the lipid bilayer?

Accepted Answer

Membrane proteins exhibit asymmetric orientation and cannot move from one monolayer to the other

Question 18

Which of the following is a plausible consequence of disrupting the hydrophobic interior of the lipid bilayer with detergents?

Accepted Answer

Integral membrane proteins lose their 3D shape and biological function

Question 19

Which of the following best describes the mechanism by which cholesterol decreases membrane permeability to ions and small polar molecules?

Accepted Answer

Cholesterol fills spaces between hydrocarbon chains of phospholipids, blocking routes for ions and small molecules

Question 20

Which of the following best explains why lateral diffusion of phospholipids occurs much more frequently than transverse diffusion (flip-flop)?

Accepted Answer

Lateral diffusion requires less energy because the hydrophilic head does not cross the hydrophobic interior

Membranes: Structure, Function, and Chemistry – Study Guide

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