Question 1

Which experimental finding provided the strongest evidence that biological membranes are composed of a lipid bilayer rather than a monolayer?

Accepted Answer

The finding that the surface area of lipids extracted from red blood cells was twice the surface area of the cells themselves.

Question 2

A researcher labels the lipids in a cell membrane with a fluorescent dye and then uses a laser to bleach a small area. Over time, the bleached area disappears. What property of the membrane does this experiment demonstrate?

Accepted Answer

The lateral diffusion of lipids within the membrane.

Question 3

Which of the following best explains why transverse diffusion (flip-flop) of phospholipids is rare in artificial bilayers but more common in living cells?

Accepted Answer

Cells contain flippase proteins that catalyze the transverse diffusion of lipids.

Question 4

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

Accepted Answer

Increasing the proportion of unsaturated fatty acids.

Question 5

A plasma membrane is found to contain a high percentage of glycolipids in its outer monolayer. What is the most likely function of these glycolipids?

Accepted Answer

Participating in cell-cell recognition and signaling.

Question 6

Which of the following statements about cholesterol in animal cell membranes is TRUE?

Accepted Answer

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

Question 7

Which of the following best describes the structure of a typical integral membrane protein?

Accepted Answer

It contains one or more hydrophobic segments that span the lipid bilayer.

Question 8

A mutation causes a cell to produce only saturated fatty acids in its membrane phospholipids. What is the most likely effect on the cell at normal body temperature?

Accepted Answer

The membrane will become less fluid and more rigid.

Question 9

Which of the following is a function of the carbohydrate chains attached to glycoproteins in the plasma membrane?

Accepted Answer

Serving as recognition sites for cell-cell interactions.

Question 10

Which of the following best explains why membrane proteins cannot move from one side of the bilayer to the other after they are inserted?

Accepted Answer

The hydrophobic core of the membrane prevents the passage of hydrophilic protein regions.

Question 11

Which of the following equations correctly describes the relationship between the transition temperature $$T_m$$ and the number of double bonds in fatty acids (all 18-carbon fatty acids)?

Accepted Answer

$$T_m$$ decreases as the number of double bonds increases.

Question 12

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

Accepted Answer

Sphingolipids contain a sphingosine backbone.

Question 13

Which of the following best describes the effect of increasing the length of fatty acid chains in membrane phospholipids?

Accepted Answer

It decreases membrane fluidity.

Question 14

Which of the following is TRUE regarding the asymmetry of biological membranes?

Accepted Answer

Asymmetry is established during membrane synthesis and is maintained over time.

Question 15

Which of the following is a common sugar found in glycoproteins of the plasma membrane?

Accepted Answer

Galactose

Question 16

Which of the following best describes the role of sterols in eukaryotic cell membranes?

Accepted Answer

They stabilize membrane fluidity across temperature changes.

Question 17

Which of the following is a property of peripheral membrane proteins?

Accepted Answer

They are hydrophilic and associate with the membrane surface.

Question 18

Which of the following is a direct consequence of the amphipathic nature of phospholipids?

Accepted Answer

They spontaneously form bilayers in aqueous environments.

Question 19

Which of the following best explains why the protein:lipid ratio varies considerably in membranes from different sources?

Accepted Answer

Different membranes have different functional requirements, leading to variation in protein content.

Membranes: Structure, Function, and Chemistry – Study Guide

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