Question 1

Which experiment provided the first quantitative evidence for the lipid bilayer structure of biological membranes?

Accepted Answer

Gorter and Grendel's extraction of lipids from red blood cells and calculation of surface area

Question 2

The image below (first image) shows a trilaminar pattern observed in electron microscopy of cell membranes. What does this pattern primarily represent?

Accepted Answer

A lipid bilayer with associated proteins on both sides

Question 3

Which of the following best describes the role of cholesterol in the plasma membrane at different temperatures?

Accepted Answer

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

Question 4

A membrane is enriched in stearate (a saturated fatty acid). What would you expect to observe in a differential scanning calorimetry experiment?

Accepted Answer

A higher transition temperature ($$T_m) $$compared to normal membranes

Question 5

Which of the following statements about lipid rafts is correct?

Accepted Answer

They are specialized membrane domains enriched in saturated fatty acids, cholesterol, and specific proteins.

Question 6

Which enzyme is responsible for the 'flip-flop' movement of phospholipids between the two leaflets of a biological membrane?

Accepted Answer

Flippase (phospholipid translocase)

Question 7

A mutation causes a membrane protein to lose all hydrophobic amino acids in its transmembrane domain. What is the most likely consequence?

Accepted Answer

The protein will be unable to span the membrane and may misfold or be degraded.

Question 8

Which of the following best explains why different membranes within the same cell have different lipid and protein compositions?

Accepted Answer

Different functions require different compositions for optimal activity.

Question 9

Which method allows for the visualization of membrane proteins by splitting the bilayer and observing the exposed interior surfaces?

Accepted Answer

Freeze-fracture electron microscopy

Question 10

A transmembrane protein has a segment (amino acids 200-400) that forms a tight ball with minimal exposure to the cytoplasm. What is the most likely property of the amino acids in this segment?

Accepted Answer

They are predominantly hydrophobic.

Question 11

Which of the following is a correct statement about the fluid mosaic model of membrane structure?

Accepted Answer

Lipids and proteins can move laterally within the plane of the membrane.

Question 12

Which property of fatty acids will most increase the fluidity of a biological membrane?

Accepted Answer

Increasing the number of double bonds (unsaturation)

Question 13

Which of the following best describes the effect of cholesterol on membrane phase transition temperature ($$T_m$$)?

Accepted Answer

Cholesterol broadens the phase transition, making the membrane less sensitive to temperature changes.

Question 14

Which of the following experimental techniques is used to separate membrane proteins based on their size after solubilization with SDS?

Accepted Answer

SDS-PAGE (polyacrylamide gel electrophoresis)

Question 15

A patient has a genetic defect that reduces the amount of cholesterol in their plasma membranes. Which of the following symptoms would you most likely expect in cold environments?

Accepted Answer

Increased membrane rigidity and possible gelling of membranes

Question 16

Which of the following interactions is NOT a major way cholesterol interacts with phospholipids in the membrane?

Accepted Answer

Covalent bonds

Question 17

Which of the following best explains why the plasma membrane of a neuron contains a higher proportion of lipids compared to the mitochondrial inner membrane?

Accepted Answer

Neuronal membranes require more insulation and flexibility for signal transmission.

Question 18

Which of the following is a function primarily associated with membrane proteins rather than the lipid bilayer?

Accepted Answer

Transport and signaling

Question 19

Which of the following statements about the movement of lipids in biological membranes is correct?

Accepted Answer

Transverse diffusion (flip-flop) is slow and often requires flippase enzymes.

Question 20

A scientist uses atomic force microscopy to study a cell membrane. What type of information can this technique provide?

Accepted Answer

The topography and mechanical properties of membrane domains such as lipid rafts

Structure and Function of Biological Membranes

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