Wiley ch. 8

You measure the transition (melting) temperature of membranes isolated from bacterial cells. This temperature is higher for Sample A than for Sample B. Which of the following could explain this difference A. Cells in Sample A were grown at 25°C whereas those in Sample B were grown at 37°C. B. The lipids from Sample A contain a greater proportion of long chain fatty acids. C. The lipids from Sample B contain a greater proportion of saturated fatty acids. D. Both A and C could explain the difference.

B. The lipids from Sample A contain a greater proportion of long chain fatty acids.

Which type of movement occurs most slowly in a bilayer lipid? transverse diffusion lateral diffusion bending rotation

transverse diffusion

Which of the following fatty acids has the highest melting temperature? 18:0 16:0 16:1 18:1

18:0

Which of the following forms micelles spontaneously in water? Cholesterol Fatty acids Triacylglycerols Glycerophospholipids

Fatty Acids

Which of the following forms bilayers spontaneously in water? Fatty acids Cholesterol Triacylglycerols Glycerophospholipids

Glycerophospholipids

Lipids with branched chains are derived from cholesterol. vitamin D. glycerol. isoprene.

Isoprene

For biological membranes the transition from the ordered crystalline state to the fluid state occurs over a broad temperature range rather than as a sharp transition. Why? a- Biological membranes contain complex mixtures of lipids. b- Biological membranes are stabilized by covalent bonds. c- Biological membranes have a homogenous glycerophospholipid content. d- Biological membranes lack cholesterol.

a- Biological membranes contain complex mixtures of lipids.

Which of the following types of molecular movement is least common in biological membranes? a- Diffusion (flip-flop) of phospholipids from one side of the bilayer to the other. b- Lateral diffusion of phospholipids in the bilayer. c- Lateral diffusion of peripheral membrane proteins in the bilayer. d- Random movement of the acyl side chains within the phospholipid bilayer. e- Diffusion of small non-polar molecules through the bilayer.

a- Diffusion (flip-flop) of phospholipids from one side of the bilayer to the other.

Which one of the following sequences of five amino acids would most likely be located on the surface of the transmembrane portion of an integral membrane protein? a- Met-Phe-Pro-Ile-Leu b- Tyr-Phe-Glu-Asn-Leu c- Glu-Asn-Ser-Thr-Gln d- Val-Thr-Val-Glu-Val

a- Met-Phe-Pro-Ile-Leu

In the laboratory, bacteria are typically grown at a temperature of 37°C. What happens to the membrane lipid composition if the temperature is increased to 42°C? a- The membrane becomes enriched in fatty acids with more carbons and with fewer double bonds. b- The membrane becomes enriched in fatty acids with less carbons and with fewer double bonds. c- The membrane becomes enriched in fatty acids with more carbons and more double bonds. d- The membrane becomes enriched in fatty acids with less carbons and more double bonds.

a- The membrane becomes enriched in fatty acids with more carbons and with fewer double bonds. --> Increasing the temperature would make the membrane more fluid. To maintain constant fluidity, the bacteria synthesize fatty acids with more carbons and with fewer double bonds.

In a membrane protein that forms a β barrel, a- protein backbone groups form hydrogen bonds. b- the openings of the barrel are blocked by peripheral membrane proteins. c- the center of the barrel contains an α helix. d- the side chains are covalently linked to lipids.

a- protein backbone groups form hydrogen bonds.

Which one of the following is a general feature of the lipid bilayer in all biological membranes? a- Polar, but uncharged, compounds readily diffuse across the bilayer. b- Individual lipid molecules are free to diffuse laterally in the bilayer. c- Individual lipid molecules in one face (monolayer) of the bilayer readily diffuse (flip-flop) to the other monolayer. d- The bilayer is stabilized by covalent bonds between neighboring phospholipid molecules.

b- Individual lipid molecules are free to diffuse laterally in the bilayer.

The composition of most membranes can be described as a- mostly lipid. b- approximately equal amounts of protein and lipid. c- mostly protein.

b- approximately equal amounts of protein and lipid.

Which of the following statements about the composition of biological membranes is TRUE? a- Triacylglycerols are a major component of all membranes. b- All proteins are excluded from lipid membranes. c- Peripheral membrane proteins associate non-covalently with lipid head groups in the bilayer. d- All biological membranes contain cholesterol. e- The lipid composition of all membranes in eukaryotic cells is the same.

c- Peripheral membrane proteins associate non-covalently with lipid head groups in the bilayer.

Which of the following statements CORRECTLY describes triacylglycerols? a- Triacylglycerols always contain three identical esterified fatty acids. b- Triacylglycerols are amphiphilic molecules. c- Triacylglycerols form lipid bilayers in aqueous solutions. d- Triacylglycerols have a polar head group. e- Triacylglycerols are molecules of energy storage.

e- Triacylglycerols are molecules of energy storage.

In preparation for hibernation, ground squirrels tend to increase the proportion of unsaturated fatty acids incorporated into their membrane lipids. Given that the animals must survive a significant drop in body temperature during hibernation, which of the following statements correctly explains why this particular change in fatty acid composition occurs?a- The fluidity of the squirrels' cell membranes must be increased, and unsaturated fatty acids assist in this because they have more van der Waal's interactions between them than saturated fatty acids. b- the fluidity of the squirrels' cell membranes must be decreased, and unsaturated fatty acids assist in this because they have more van der Waal's interactions between them than saturated fatty acids. c- The fluidity of the squirrels' cell membranes must be increased, and unsaturated fatty acids assist in this because they have fewer van der Waal's interactions between them than saturated fatty acids. d- The fluidity of the squirrels' cell membranes must be decreased, and unsaturated fatty acids assist in this because they have fewer van der Waal's interactions between them than saturated fatty acids.

c- The fluidity of the squirrels' cell membranes must be increased, and unsaturated fatty acids assist in this because they have fewer van der Waal's interactions between them than saturated fatty acids.

A bilayer becomes more crystalline as a- the temperature increases. b- the lipids' unsaturation increases. c- the lipids' hydrocarbon length increases. d- the salt concentration increases.

c- the lipids' hydrocarbon length increases.

Which of the following statements describing cholesterol in biological membranes is TRUE? a- Cholesterol's planar ring structure is highly flexible, which maximizes its interactions with the acyl tails of neighboring lipids. b- Cholesterol is located between the polar head groups of the membrane lipids. c- Cholesterol has no effect on the stability or transition temperature of a membrane. d- Cholesterol is an important component of the plasma membrane in mammalian cells.

d- Cholesterol is an important component of the plasma membrane in mammalian cells.

Which of the following statements about membrane lipids is FALSE? a- Cholesterol inserts in between the fatty acyl tails of other membrane lipids, where it modulates the fluidity of membranes. b- Glycerophospholipids contain fatty acids linked to glycerol through ester bonds. c- Although sphingolipids and glycerophospholipids are structurally dissimilar, their 3-D shapes are similar. d- Glycerophospholipids may have a sugar molecule as their polar head group (glycolipids).

d- Glycerophospholipids may have a sugar molecule as their polar head group (glycolipids).

A triacylglycerol a- includes three acyl groups that associate noncovalently. b- is a chain of three linked fatty acid residues. c- consists of a fatty acid that has three glycerol groups esterified to it. d- is the product of three condensation reactions.

d- is the product of three condensation reactions.

According to the fluid mosaic model of membrane structure, a- lipids diffuse laterally while proteins are stationary. b- proteins form rafts that float on top of the lipids. c- proteins form repeating patterns like a mosaic. d- lipids and proteins are distributed asymmetrically.

d- lipids and proteins are distributed asymmetrically.

Rank the melting points of the following fatty acids: a. cis-oleate (18:1); b. trans-oleate (18:1); c. linoleate (18:2). a. cis-oleate (18:1) > trans-oleate (18:1) > linoleate (18:2) b. cis-oleate (18:1) < trans-oleate (18:1) < linoleate (18:2) c. trans-oleate (18:1) < cis-oleate (18:1) < linoleate (18:2) d. linoleate (18:2) < cis-oleate (18:1) < trans-oleate (18:1)

d. linoleate (18:2) < cis-oleate (18:1) < trans-oleate (18:1) Smallest melting point (18:2) --> largest melting point (18:3) Trans always has a higher MP than cis