Question 1

Which of the following best explains why eukaryotic cells can compartmentalize different metabolic processes, while prokaryotic cells cannot?

Accepted Answer

Eukaryotic cells have internal membranes that create distinct organelles, whereas prokaryotic cells lack these internal membranes.

Question 2

Which of the following is NOT a function of the plasma membrane in eukaryotic cells?

Accepted Answer

Providing a rigid, inflexible structure to the cell.

Question 3

Which organelle is responsible for the synthesis of most lipids in eukaryotic cells?

Accepted Answer

Endoplasmic reticulum (ER)

Question 4

What is the main structural difference between the rough ER and the smooth ER?

Accepted Answer

The rough ER has ribosomes bound to its cytosolic surface, while the smooth ER does not.

Question 5

Which of the following best describes the amphipathic nature of membrane lipids?

Accepted Answer

They contain both hydrophilic and hydrophobic regions.

Question 6

Why do phospholipid bilayers spontaneously form sealed compartments in water?

Accepted Answer

To minimize the exposure of hydrophobic tails to water, which is energetically favorable.

Question 7

How does cholesterol affect the fluidity of the plasma membrane?

Accepted Answer

Cholesterol tends to stiffen the membrane by filling gaps between phospholipids.

Question 8

Which enzyme is responsible for the random transfer of phospholipids between monolayers in the ER membrane?

Accepted Answer

Scramblase

Question 9

What is the main reason that glycolipids are found exclusively in the noncytosolic monolayer of the plasma membrane?

Accepted Answer

Their sugar groups are added in the lumen of the Golgi and remain facing the extracellular space after vesicle fusion.

Question 10

Which of the following statements about membrane protein orientation during vesicle transport is correct?

Accepted Answer

The orientation of membrane proteins is preserved; the cytosolic side always faces the cytosol.

Question 11

Which of the following best describes the structure of a transmembrane α helix?

Accepted Answer

It contains about 20 hydrophobic amino acids that span the lipid bilayer.

Question 12

A mutation causes a membrane protein to lose its ability to form hydrogen bonds within its α helix. What is the most likely consequence?

Accepted Answer

The protein will be unable to stably span the lipid bilayer.

Question 13

Which of the following is a function of the spectrin meshwork in human red blood cells?

Accepted Answer

It provides mechanical support and maintains the biconcave shape of the cell.

Question 14

Which of the following best explains why the carbohydrate layer (glycocalyx) is found on the external surface of eukaryotic cells?

Accepted Answer

Carbohydrate groups are added to proteins and lipids in the lumen of the ER and Golgi, which becomes the external surface after vesicle fusion.

Question 15

Which of the following mechanisms can restrict the lateral mobility of plasma membrane proteins?

Accepted Answer

Tethering to the cell cortex, extracellular matrix, or other cells, and diffusion barriers such as tight junctions.

Question 16

A patient has a genetic defect in flippase enzymes. Which of the following would most likely be observed in their cells?

Accepted Answer

An abnormal distribution of phosphatidylserine and phosphatidylethanolamine between the two leaflets of the plasma membrane.

Question 17

Which of the following best describes the effect of detergents like Triton X-100 on biological membranes?

Accepted Answer

They solubilize membrane proteins by disrupting the lipid bilayer and forming protein-detergent complexes.

Question 18

Which of the following is a real-life application of the asymmetric distribution of membrane lipids in eukaryotic cells?

Accepted Answer

Exposure of phosphatidylserine on the outer leaflet of the plasma membrane serves as a signal for macrophages to engulf apoptotic cells.

Question 19

A scientist is studying a membrane protein that is only weakly associated with the membrane via noncovalent interactions with other proteins. How should this protein be classified?

Accepted Answer

Peripheral membrane protein

Cell Membranes: Structure, Composition, and Function

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