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 FALSE cholesterol is amphipathic it fits in between the phospholipids and blocks diffusion through the membrane by increasing hydrophobic interactions 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 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 b c d 11 6 Produce lipids with hydrocarbon tails that are longer and have fewer double bonds Produce lipids with hydrocarbon tails that are shorter and have more double bonds Decrease the amount of cholesterol in the membrane Decrease the amount of glycolipids in the membrane 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 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 cholesterol fatty acid tails glycolipids hydrophilic head groups 11 8 hydrophobic lipid bilayer lipid monolayer lipids phosphatidylcholine phosphatidylserine phospholipids proteins sterols sugars 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 flippase probably exist Figure Q11 8 a b c d 11 9 X only Z only X and Y Y and Z Where does most new membrane synthesis take place in a eucaryotic 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 c d acetone methanol urea 11 11 Membranes undergo spontaneous rearrangement if torn Which of the following would happen if a cell membrane had a large tear 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 flippases b phospholipases c convertases d glycosylases 11 17 Glycolipids are found on the surface of healthy cells and contribute to the cell s defense against chemical damage and infectious agents A In which organelle are sugar groups added to membrane lipids 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 Cterminus 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