CHAPTER 10 MEMBRANE STRUCTURE

1. What is the typical thickness of a lipid bilayer such as the plasma membrane of our cells?

A. 0.5 nm

B. 5 nm

C. 50 nm

D. 100 nm

E. 500 nm

1. In the following schematic drawing of an abundant plasma membrane phosphoglyceride,

which part is positively charged?

A. A

B. B

C. C

D. D

E. E

1. Which of the following is NOT correct regarding the molecule whose structural formula

is shown below?

A. It is an amphiphilic molecule.

B. It is a sterol.

C. It makes the membrane less permeable to small hydrophilic molecules.

D. It is found in membranes of virtually all living cells.

E. It affects the fluidity of the lipid bilayer.

1. Which of the following is normally NOT found in a eukaryotic membrane?

A. Cholesterol

B. Phosphatidylinositol

C. Sphingomyelin

D. Ganglioside GM1

E. Octylglucoside

1. The motion of lipid molecules in a synthetic bilayer can be studied by various techniques.

Which of the following has been observed in these systems?

A. Phospholipids diffuse rapidly within and between the two leaflets of a bilayer.

B. An average lipid molecule can diffuse the length of about 2 micrometers in a fraction

of a millisecond.

C. The flip-flops are very rare for phospholipids but cholesterol molecules flip-flop more

often.

D. Within a bilayer, lipid molecules rarely rotate about their long axis, but diffuse

laterally at very high rates.

E. All of the above.

1. Why do liposomes not fuse with one another spontaneously when suspended in an

aqueous environment?

A. Because fusion requires a large number of flip-flops, which are very rare.

B. Because the hydration shell of the polar head groups of the lipids needs to be

removed.

C. Because fusion requires micelle formation.

D. Because of the rapid lateral diffusion and rotation of the lipid molecules.

1. Which of the following changes would you expect to increase the phase transition

temperature of a synthetic bilayer composed of phosphatidylserine?

A. Incorporation of phospholipids with longer fatty acid chains.

B. Introduction of double bonds in the fatty acids.

C. Addition of cholesterol.

D. Removal of serine from the head group.

E. None of the above.

1. Which of the following is correct regarding the composition of various biological

membranes?

A. Bacterial plasma membranes are often composed of one main type of phospholipid

and lack cholesterol.

B. Cholesterol in the eukaryotic plasma membrane induces phase transition to the gel

state.

C. Inositol phospholipids are the most abundant lipids in the endoplasmic reticulum

membrane.

D. The mitochondrial and bacterial membranes are rich in glycolipids.

E. Yeast cells synthesize more fatty acids with cis-double bonds when the temperature in

the environment rises.

1. The two monolayers of the plasma membrane in a human red blood cell …

A. have different overall electrical charges, with negatively charged phospholipids (e.g.

phosphatidylserine) normally enriched in the inner monolayer.

B. have the same abundance of phosphatidylinositol.

C. exchange phospholipids only through spontaneous flip-flops.

D. both contain glycolipids.

E. both contain gangliosides.

1. Many cells store lipids in droplets of varying sizes. These droplets …

A. are enclosed by a phospholipid monolayer (instead of a bilayer).

B. mostly store cholesterol and phospholipids.

C. are produced by and released from the Golgi apparatus.

D. have mostly protein-free bilayer membranes.

E. are composed primarily of charged amphiphilic lipids.

1. Which of the following lipids do you expect to be a canonical scramblase substrate in the

plasma membrane?

A. Ganglioside GM1

B. Cholesterol

C. Glycosylphosphatidylinositol

D. Phosphatidylethanolamine

E. Galactocerebroside

1. Glycolipids such as gangliosides …

A. may contain oligosaccharide chains with negatively charged residues.

B. are found to constitute about 10% of the total lipid mass in the plasma membrane of

neurons.

C. are found in the extracellular leaflet (facing away from the cytosol) in the cellular

membranes.

D. affect the electrical environment of the membrane.

E. All of the above

1. Transmembrane proteins …

A. are typically exposed only to one side of the membrane.

B. can be released from the membrane by a gentle extraction procedure such as salt

treatment.

C. are often further attached to the membrane via a GPI anchor.

D. are sometimes covalently attached to a fatty acid chain that inserts into the membrane.

E. cannot contain β sheets in the part of their structure that interacts with the membrane

interior.

1. Integrins are single-pass integral membrane proteins in the plasma membrane of animal

cells and are involved in the interaction of the cell with the surrounding extracellular matrix.

Which of the following descriptions do you think matches the transmembrane part of an integrin

molecule?

A. It forms a β barrel.

B. It is an α helix that is bent in the middle.

C. It is about 10 amino acids long, with every other amino acid side chain being

hydrophobic.

D. It folds in a conformation with maximal intrachain hydrogen-bonding.

E. It is about 100 amino acids long.

1. The nicotinic acetylcholine receptor is a cation channel in the plasma membrane of some

neurons. It is composed of five subunits, each of which is a transmembrane protein. The

hydropathy plot for each mature subunit is qualitatively represented in the following diagram.

How many membrane-spanning alpha helices do you expect to exist in each subunit?

+25

Hydropath

y index 0

–25

1 100 200 300 400

Residue number

1. What do all β-barrel transmembrane proteins have in common?

A. The number of β strands.

B. The diameter of the barrel.

C. The number of negative peaks in their hydropathy plots.

D. The general function, i.e. membrane transport.

E. The structural rigidity compared to α-helical transmembrane proteins.