1 Biochemistry I, Fall 2005 Name:____________________________________ Biochemistry I - Exam III - Face Page The following equations and constants may be useful: ! "G = "G° + RT ln[ products][reac tan ts] ! "G° = #RT lnKEQ R = 8.3 J/mol-K T = 300K and pH = 7.0 unless otherwise stated.2 A. Multiple Choice: Please circle the best answer (2 pts each, 20 pts total). 1. The phospholipid bilayer is a) permeable to both charged and nonpolar compounds as long as they are small. b) permeable to nonpolar compounds but impermeable to charged compounds. c) permeable to charged compounds but impermeable to nonpolar compounds. d) impermeable. 2. Phospholipids are composed of a) three fatty acids esterified to glycerol. b) a head group, a phosphate group and two fatty acids esterified to glycerol. c) a head group, two fatty acids and a phosphate group linked to glycerol by a phosphoanhydride bond. d) cholesterol and two fatty acid chains. 3. Phospholipids a) always have a net negative charge. b) can be zwitterionic. c) can have a net negative charge. d) Both b and c. 4. The fluidity of a biological membrane can be increased by _________ the length of phospholipid acyl chains, _________ the number of cis-double bonds in the acyl chains, as well as _________ the concentration of cholesterol in the membrane. a) increasing, decreasing, increasing b) decreasing, increasing, increasing c) increasing, increasing, decreasing d) decreasing, decreasing, decreasing 5. The structure shown below is a(n) _______ called _______. a) aldose, glucose b) aldose, ribose c) aldose, fructose d) ketose, fructose 6. The disaccharide shown below is a(n) _____ linkage and is found in _____. a) α(1-4), cellulose b) β(1-4), cellulose c) α(1-4), glycogen d) β(1-4), bacterial cell walls. OOOOCH2OHCH2OHOOHOHOHOHOCH2OHOHOHCH2OH3 7. The progressive oxidation of glucose to CO2 involves a) the loss of electrons from glucose and the oxidation of NADH. b) the loss of electrons from glucose and the reduction of NAD+. c) the gain of electrons by glucose and the oxidation of NADH. d) the gain of electrons by glucose and the reduction of NAD+. 8. In a eukaryotic cell, the enzymes of glycolysis are located in the _______, and the enzymes involved in electron transport are located in the _________. a) mitochondrial matrix, inner mitochondrial membrane b) cytosol, mitochondrial matrix c) cytosol, inner mitochondrial membrane d) mitochondrial matrix, cytosol 9. Fatty acids provide a rich source of energy when they are completely oxidized a) to glucose via gluconeogenesis. b) to CO2 via the TCA cycle. c) to CO2 by pyruvate dehydrogenase. d) to fumarate via the electron transport chain. 10. Under anaerobic conditions, a) NAD+ is regenerated by reduction of pyruvate to lactate. b) NADH is regenerated by reduction of pyruvate to lactate. c) NAD+ is regenerated by oxidation of lactate to pyruvate. d) NADH is regenerated by oxidation of lactate to pyruvate. B. 1. (12 pts) For two of the three reactions shown below, list the general type of reaction (ie, reduction, phosphorylation, etc), the pathway in which the reaction takes place, and at least one cofactor or co-substrate for the reaction. i) ii) iii) OCH2OHOHOHOHOHOCH2OPO3-2OHOHOHOHRCOSCoARCOSCoAOHHOOHOHCH2OPO3-2HOHCH2OPO3-2HOOPO3-24 2. (12 pts) Please choose two of the following three questions. Choice A: Briefly distinguish product inhibition from feedback inhibition and provide one example of either from glycolysis or the TCA cycle. Include the name of the enzyme and its regulator in your answer. Choice B: Briefly describe how metabolic enzymes are regulated by cellular energy status. Provide the name of one such enzyme and its regulator. Choice C: List three common features of metabolic enzymes whose activities are regulated. 3. (10 pts) i) Briefly discuss the major energetic term that drives formation of the phospholipid bilayer. (5 pts) ii) (5 pts) Choose one of the following two questions. Choice A: Briefly discuss the importance of membrane fluidity in a biological process such as electron transport. Choice B: Briefly discuss the importance of the impermeability of the inner mitochondrial membrane in ATP synthesis.5 4. (10 pts) Several key steps in glycolysis are catalyzed by kinases. i) Indicate the enzyme, substrate(s) and product(s) for one of these reactions. (3 pts) [A drawing of the structure of the substrate may be helpful but not required]. ii) Briefly explain how direct coupling is used to reduce the overall ΔG° of the reaction. (4pts) iii) The reverse of a phosphorylation reaction is a de-phosphorylation reaction. Briefly explain why removal of a phosphate group from a substrate does not require an input of energy. (3 pts) 5. (10 pts) Consider the following hypothetical metabolic pathway: i) (5 pts) The conversion of A to B has a positive ΔG°; yet there is net conversion of A to B during the normal functioning of the pathway in cells. Explain how this is likely to occur. ii) (5 pts) Choose one of the following two questions concerning the above pathway: Choice A: The conversion of A to B has a ΔG° of 10 kJ/mol but a Gibbs free energy of -5 kJ/mol. What is the ratio of B:A under these conditions? Choice B: What is the equilibrium ratio of B:A under standard state conditions? ABCEnzyme 1Enzyme 26 6. (6 pts) The energy obtained from the oxidation of glucose is stored in several “high energy intermediates” before final conversion to ATP. List 3 of these “intermediates”. 7. (10 pts) Please choose one of the following two questions. You need not list every single step, just the key steps such that your explanation makes sense. Choice A: Describe how low blood glucose levels leads to the (coordinate) activation of glycogen breakdown and inhibition of glycogen synthesis in a liver cell. Choice B: Describe how low blood glucose leads to the (coordinate) inhibition of glycolysis and activation of gluconeogenesis in a liver cell.7 8. (10 pts) Choose one of the following two questions. A well-labeled diagram is an acceptable answer. Choice A: Describe the electron transport process, beginning with NADH and ending with the reduction of O2. Do not discuss the mechanism of ATP synthesis. Choice B: Discuss the