Chapter 12 Lipids and Cell Membranes 6 Short-Answer Questions 16 What does the notation 18:2 for fatty acids imply? Ans:In this fatty acid there are 18 carbons,with 2 double bonds. Section:12.1 17 What are the two systems for naming the positions of the double bonds?Provide examples. Ans:Two systems are used.One system refers to the double bond relative to the last,or omega ()carbon.(An example would be c-3 fatty acids.)The other system uses notation that indicates the position of the double bond relative to the carboxyl carbon,and indicates if the bond is cis or trans.(An example would be cis-A.) Section:12.1 18 What are some molecules that form the polar head group of a phospholipids?Provide several examples. Ans:Examples of head groups include serine,ethanolamine,choline,glycerol,and inositol. Section:12.2 19 What is cardiolipin? Ans:This is a molecule in which two phospholipids are attached through the phosphate groups to a glycerol molecule.It is also called diphosphatidyl glycerol. Section:12.2 20 Draw a cross-section of a micelle and a membrane bilayer. Ans:Micelles are spherical arrangements in which the tails are on the inside of the sphere,and the heads are on the outside surface.Bilayers have two lipid layers,in which the heads are on the outside,and the tails are arranged on the inside in two rows.Figures 12.9 and 12.10 in the textbook provide an example of this. Section:12.3 21 Draw and label a typical phospholipid Ans: The phospholipid drawn should resemble Figure 12.5 in the textbook.It should contain a central glycerol molecule,to which two fatty acids are attached in ester linkages at the center and an end.The other end should be linked to a phosphor alcohol group.The phosphate should be shown negatively charged at pH 7. HH CH2-0-C(CH2)14CH3 CH3(CH2)C=C(CH2)C-0-CH CH2-OPOCH2CH2N(CH3)3 0 Section:12.2 22 How are lipid bilayers formed?What is the driving force? Ans:Bimolecular sheets of lipids form spontaneously by self-assembly.Hydrophobic interactions are the driving force.Van der Waals attractive forces between the hydrocarbon tails favor the close packing of the tails.The polar heads are attracted to each other by electrostatic and hydrogen-bonding attractions. Section:12.4Chapter 12 Lipids and Cell Membranes 6 Short-Answer Questions 16 What does the notation 18:2 for fatty acids imply? Ans: In this fatty acid there are 18 carbons, with 2 double bonds. Section: 12.1 17 What are the two systems for naming the positions of the double bonds? Provide examples. Ans: Two systems are used. One system refers to the double bond relative to the last, or omega (), carbon. (An example would be -3 fatty acids.) The other system uses notation that indicates the position of the double bond relative to the carboxyl carbon, and indicates if the bond is cis or trans. (An example would be cis- 9 .) Section: 12.1 18 What are some molecules that form the polar head group of a phospholipids? Provide several examples. Ans: Examples of head groups include serine, ethanolamine, choline, glycerol, and inositol. Section: 12.2 19 What is cardiolipin? Ans: This is a molecule in which two phospholipids are attached through the phosphate groups to a glycerol molecule. It is also called diphosphatidyl glycerol. Section: 12.2 20 Draw a cross-section of a micelle and a membrane bilayer. Ans: Micelles are spherical arrangements in which the tails are on the inside of the sphere, and the heads are on the outside surface. Bilayers have two lipid layers, in which the heads are on the outside, and the tails are arranged on the inside in two rows. Figures 12.9 and 12.10 in the textbook provide an example of this. Section: 12.3 21 Draw and label a typical phospholipid. Ans: The phospholipid drawn should resemble Figure 12.5 in the textbook. It should contain a central glycerol molecule, to which two fatty acids are attached in ester linkages at the center and an end. The other end should be linked to a phosphor alcohol group. The phosphate should be shown negatively charged at pH 7. + C H 2 C H C H 2 O C(C H 2 )14C H 3 O C H 3 (C H 2 )7C C(C H 2 )7C O O H H O PO C H 2C H 2N (C H 3 )3 O O - Section: 12.2 22 How are lipid bilayers formed? What is the driving force? Ans: Bimolecular sheets of lipids form spontaneously by self-assembly. Hydrophobic interactions are the driving force. Van der Waals attractive forces between the hydrocarbon tails favor the close packing of the tails. The polar heads are attracted to each other by electrostatic and hydrogen-bonding attractions. Section: 12.4