Question 1

Based on your knowledge of the chemistry of the cell membrane, which of the following compounds would you couple with a new drug in order to achieve better uptake by cells?

Accepted Answer

Lipids are a major component of cell membranes, and coupling a drug with lipids can enhance its ability to integrate into the lipid bilayer, improving uptake by cells.

Question 2

You are experimenting with a variety of lipids to determine their efficacy for use as drug delivery system liposomes. What is one feature of the individual lipid that would best ensure the use of a lipid for this purpose?

Accepted Answer

Lipids used in liposomes for drug delivery should be amphipathic, meaning they have both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts. This allows them to form bilayers, which are essential for creating stable liposome structures that can encapsulate drugs.

Question 3

Which of the following molecules would NOT readily cross an intact cell membrane by simple diffusion?

Accepted Answer

Glucose is a large polar molecule and does not readily cross cell membranes by simple diffusion; it requires transport proteins.

Question 4

To facilitate the regulation of membrane fluidity, E.coli has the enzyme

Accepted Answer

Desaturase is an enzyme that introduces double bonds into fatty acids, which helps regulate membrane fluidity by increasing unsaturation in the lipid bilayer.

Question 5

Two cells with different cell- surface markers are fused in the presence of polyethylene glycol (PEG). The cells are then placed at 0°C. What do you expect to observe about the individual cell markers?

Accepted Answer

At 0°C, the fluidity of the cell membrane is reduced, so the cell-surface markers will remain in their original positions with little migration.

Question 6

Which of the following is a sterol- like lipid associated with the cell membrane of prokaryotes?

Accepted Answer

Hopanoids are sterol-like molecules found in the cell membranes of some prokaryotes, providing structural stability similar to cholesterol in eukaryotic membranes.

Question 7

With regard to the semipermeable nature of the plasma membrane, which of the following would readily cross without the aid of a transport protein?

Accepted Answer

Water can readily cross the plasma membrane through simple diffusion due to its small size and polarity, even though it is polar.

Question 8

The most common number of carbons in fatty acid hydrocarbon chains of membrane phospholipids is

Accepted Answer

The most common number of carbons in fatty acid hydrocarbon chains of membrane phospholipids is 16, as seen in palmitic acid, a prevalent saturated fatty acid in biological membranes.

Question 9

A means of detecting the presence of specific carbohydrate moieties on glycoproteins is

Accepted Answer

Lectins are proteins that bind specifically to certain sugars and can be conjugated with markers like ferritin to detect carbohydrate moieties on glycoproteins.

Question 10

Which of the following disorders is the result of impaired glycosphingolipid metabolism?

Accepted Answer

Tay-Sachs disease is a genetic disorder caused by the accumulation of glycosphingolipids due to a deficiency in the enzyme hexosaminidase A, which is crucial for their metabolism.

Question 11

Starting with shredded spinach leaves, you follow a procedure that allows for separation of cellular organelles. You are specifically looking for the fraction that contains the mitochondria. To identify this fraction you should test for the

Accepted Answer

Mitochondria are involved in cellular respiration, so testing for enzymes associated with this process, such as those in the electron transport chain or the Krebs cycle, would help identify the mitochondrial fraction.

Question 12

With respect to the outer and inner faces of the lipid bilayer of the cell membrane, the composition of lipids is

Accepted Answer

The lipid bilayer of the cell membrane is asymmetrical, meaning that the composition of lipids differs between the outer and inner leaflets. This asymmetry is crucial for various cellular functions, including membrane curvature, cell signaling, and the maintenance of membrane potential.

Question 13

The likely number of and locations of transmembrane segments of integral membrane proteins is inferred by

Accepted Answer

Hydropathy analysis is a method used to predict the transmembrane segments of integral membrane proteins based on the hydrophobicity of the amino acid sequence.

Question 14

Where would you expect to find an organism possessing a cell membrane with the following composition: large proportions of cholesterol and a predominance of unsaturated fatty acids?

Accepted Answer

Organisms in frozen wastelands need cell membranes that remain fluid at low temperatures, which is achieved by having unsaturated fatty acids and cholesterol.

Question 15

A prokaryotic organism is isolated from a hydrothermal vent, where it has been observed to be thriving. Based on your knowledge of the plasma membrane, you would expect to find a predominance of

Accepted Answer

Prokaryotic organisms from extreme environments like hydrothermal vents often have largely saturated fatty acids in their membranes to maintain stability and functionality at high temperatures.

Question 16

Cholesterol

Accepted Answer

Cholesterol intercalates between the fatty acid chains within the lipid bilayer of cell membranes, helping to modulate fluidity and stability. It is not found in abundance in prokaryotic cell membranes and is not exclusive to plants.

Question 17

Which is NOT a model for membrane structure?

Accepted Answer

The Watson and Crick double helix is a model for DNA structure, not membrane structure.

Question 18

A prokaryotic organism is isolated from a glacier, where it has been observed to be thriving. Based on your knowledge of the plasma membrane, you would expect to find a predominance of

Accepted Answer

Organisms in cold environments typically have largely unsaturated fatty acids in their membranes to maintain fluidity at low temperatures.

Question 19

Which of the following is NOT a function of membranes?

Accepted Answer

Information storage is not a function of membranes.

Question 20

With respect to the outer and inner faces of the lipid bilayer of the cell membrane, the composition of proteins is

Accepted Answer

The composition of proteins in the lipid bilayer is asymmetrical, meaning that the types and distributions of proteins differ between the inner and outer faces of the membrane. This asymmetry is crucial for the membrane's function, including cell signaling and transport.

Quiz 7: Membranes: Their Structure, Function, and Chemistry