Biology Chapter 11 Solved Question: The Lipid Bilayer (Other (Not Listed) Sample)

CHAPTER 11
MEMBRANE STRUCTURE
( 2009 Garland Science Publishing
The Lipid Bilayer
11-1 Indicate whether the following statements are true or false. If a statement is false, explain why it is false.
A. Although cholesterol is a hydrophobic molecule, it has a hydrophilic head group like all other membrane lipids.
B. Phosphatidylserine is the most abundant type of phospholipid found in cell membranes.
C. Glycolipids lack the glycerol component found in phospholipids.
D. The highly ordered structure of the lipid bilayer makes its generation and maintenance energetically unfavorable.
SOLUTION/ANSWER
A: true,

B: false (phosphatidylcholine is the most abundant phospholipid.)

C: true,
D: false (formation of lipid bilayer is favorable in water.)
11-2 Which of the following membrane lipids does not contain a fatty acid tail?
(a) Phosphatidylcholine
(b) A glycolipid
(c) Phosphatidylserine
(d) Cholesterol
11-3 Formation of a lipid bilayer might seem to be energetically unfavorable. However, this arrangement is actually favored because it allows a higher level of entropy than any other alternative. What makes bilayer formation energetically favorable?
(a) Polar head groups form a hydrogen bonding network at the interface with water.
(b) Water molecules form cage-like structures around hydrophobic molecules.
(c) Hydrogen bonds form between neighboring polar head groups in the bilayer.
(d) Fatty acid tails are highly saturated and flexible.
11-4 Which of the following statements is true?
(a) Phospholipids will spontaneously form liposomes in nonpolar solvents.
(b) In eucaryotes, all membrane-enclosed organelles are surrounded by one lipid bilayer.
(c) Membrane lipids diffuse within the plane of the membrane.
(d) Membrane lipids frequently flip-flop between one monolayer and the other.
11-5 A bacterium is suddenly expelled from a warm human intestine into the cold world outside. Which of the following adjustments might the bacterium make to maintain the same level of membrane fluidity?
(a) Produce lipids with hydrocarbon tails that are longer and have fewer double bonds.
(b) Produce lipids with hydrocarbon tails that are shorter and have more double bonds.
(c) Decrease the amount of cholesterol in the membrane.
(d) Decrease the amount of glycolipids in the membrane.
11-6 Three different membrane components are shown in Figure Q11-6. Using the list below, identify the three components, and label the chemical groups indicated.
A. glycerol
B. sugar
C. phospholipid
D. glycolipid
E. sterol
F. unsaturated hydrocarbon
G. saturated hydrocarbon
H. sterol polar head group

ANSWER (According to the diagrams from left to right)
B, D and E (values from the list provided above)
Figure Q11-6
11-7 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; each word or phrase should be used only once.
The specialized functions of different membranes are largely determined by the __________________ they contain. Membrane lipids are __________________ molecules, composed of a hydrophilic portion and a hydrophobic portion. All cell membranes have the same __________________ structure, with the __________________ of the phospholipids facing into the interior of the membrane and the __________________ on the outside. The most common lipids in most cell membranes are the __________________. The head group of a glycolipid is composed of __________________.
Amphipathic hydrophobic Phosphatidylserine
Cholesterol lipid bilayer phospholipids
Fatty acid tails lipid monolayer proteins
Glycolipids lipids sterols
Hydrophilic head groups phosphatidylcholine sugars
ANSWERS (According to gaps from beginning respectively)
1. Proteins2. Amphipathic 3. Lipid bi-layer4. Fatty acid tails 5. Hydrophilic head groups 6. Phospholipids. 7. Sugars.
11-8 Three phospholipids X, Y, and Z are distributed in the plasma membrane as indicated in Figure Q11-8. For which of these phospholipids does a lipase probably exist?

Figure Q11-8
(a) X only
(b) Z only
(c) X and Y
(d) Y and Z
11-9 Where does most new membrane synthesis take place in a eukaryotic cell?
(a) In the Golgi apparatus
(b) In the endoplasmic reticulum
(c) In the plasma membrane
(d) In the mitochondria
(e) On ribosomes
11-10 Water molecules readily form hydrogen bonds with other polar molecules, and when they encounter nonpolar molecules they must form hydrogen-bonding networks with neighboring water molecules. Which of the following molecules will cause a “cage” of water to form?
(a) 2-methylpropane
(b) Acetone
(c) Methanol
(d) Urea
11-11 Membranes undergo spontaneous rearrangement if torn. Which of the following would happen if a cell membrane had a large tear?

ANSWER
(C) Vesicles form
11-12 Membrane lipids are capable of many different types of movement. Which of these does not occur spontaneously in biological membranes?
(a) Switching between lipid layers
(b) Lateral movement
(c) Rotation
(d) Flexing of hydrocarbon chains
11-13 there are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. The degree of packing, in turn, influences the relative mobility of these molecules in the membrane. Which of the following would yield the most highly mobile phospholipid (listed as number of carbons and number of double bonds, respectively)?
(a) 24 carbons with 1 double bond
(b) 15 carbons with 2 double bonds
(c) 20 carbons with 2 double bonds
(d) 16 carbons with no double bonds
11-14 Cholesterol serves several essential functions in mammalian cells. Which of the following is not influenced by cholesterol?
(a) Membrane permeability
(b) Membrane fluidity
(c) Membrane rigidity
(d) Membrane thickness
11-15 new membrane phospholipids are synthesized by enzymes bound to the _____________ side of the _________________ membrane.
(a) Cytosolic, mitochondrial
(b) Luminal, Golgi
(c) Cytosolic, endoplasmic reticulum
(d) Extracellular, plasma
11-16 Membrane synthesis in the cell requires the regulation of growth for both halves of the bilayer and the selective retention of certain types of lipids on one side or the other. Which group of enzymes accomplishes both of these tasks?
(a) Lipases
(b) Phospholipases
(c) Converses
(d) Glycosylates
11-17 Glycolipids are found on the surface of healthy cells, and contribute to the cell’s defense against chemical damage and infectious agents.
In which organelle are sugar groups added to membrane lipids?
ANSWER
Golgi
B. By what mechanism are glycolipids transported to the plasma membrane and presented to the extracellular environment?
Draw a diagram to support your answer to part B.
Membrane Proteins
11-18 A group of membrane proteins can be extracted from membranes only by using detergents. All the proteins in this group have a similar amino acid sequence at their C-terminus: -KKKKKXXC (where K stands for lysine, X stands for any amino acid, and C stands for cysteine). This sequence is essential for their attachment to the membrane. What is the most likely way in which the C-terminal sequence attaches these proteins to the membrane?
(a)The cysteine residue is covalently attached to a membrane lipid.
(b)The peptide spans the membrane as and α helix.
(c)The peptide spans the membrane as part of a β sheet.
(d)The positively charged lysine residues interact with an acidic integral membrane protein.
11-19although membrane proteins contribute roughly 50% of the total mass of the membrane, there are about 50 times more lipid molecules than there are protein molecules in cellular membranes. Explain this apparent discrepancy.

ANSWER

Membrane proteins are much larger molecules than the membrane lipids. Thus, fewer are required to represent the same total mass contributed by the lipid components of the membrane. By this estimation, the molecular weight of the average membrane protein is 50 times that of the average membrane lipid.
11-20 indicate whether the following statements are true or false. If a statement is false.
Lipid-linked proteins are classified as peripheral membrane proteins because the polypeptide chain does not pass through the bilayer.
False
A protein can be embedded on the cytosolic side of the membrane bilayer by employing a hydrophobic α helix.
False
A protein that relies on protein–protein interactions to stabilize its membrane association is classified as a peripheral membrane protein because it can be dissociated without the use of detergents.
True
Membrane proteins that pump ions in and out of the cell are classified as enzymes.
False
11-21 A small membrane vesicle containing a Tran’s membrane protein is shown in Figure Q11-21. Assume that this membrane vesicle is in the cytoplasm of a cell.

Figure Q11-21
Label the cytosolic and non-cytosolic faces of the membrane vesicle. This membrane vesicle will undergo fusion with the plasma membrane.
B. Sketch the plasma membrane after vesicle fusion, indicating the new location of the vesicle membrane and the Trans membrane protein carried by the membrane vesicle.
C. On your drawing for B, label the original cytosolic and no cytosolic faces of the vesicle membrane as it resides in the plasma membrane. Also label the extracellular space and the cytosol. Indicate the N- and C-terminus of the inserted Trans membrane protein.
ANSWER
11-22Poring proteins form large, barrel-like channels in the membrane. Which of the following is not true about these channels?
(a)...