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44106a_E3 - name BICH 441 EXAM 3 An Aggie does not lie...

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Unformatted text preview: name ________________________________________ BICH 441 EXAM 3 April 27, 2006 An Aggie does not lie, cheat, or steal, or tolerate those who do. I swear on my honor as an Aggie that I have not received or given unauthorized aid on this exam, and I am not aware of others who have received or given unauthorized aid on this exam. signed _________________________________________________________ NO CALCULATORS! Before you begin, write your name on each page (there are 6 pages) and sign the Aggie Honor Code statement above. Questions 1-15 (2 pts each). Enter your answer on your Scantron sheet. 1. Which of the following is true concerning concerning utilization of fat stored in adipose cells? A. Free fatty acids are released in response to insulin. B. Adipose cells package triacylglycerol into chylomicrons for transport to other tissues. C. Triacylglycerol lipase is activated by glucagon. D. all of the above 2. A saturated fatty acid containing 18 carbon atoms is taken up by a muscle cell and converted to acetyl-CoA via the fatty acid β-oxidation pathway. Assuming that NADH and FADH2 can be used to generate 2.5 and 1.5 ATPs, respectively, via mtochondrial electron transport and oxidative phosphorylation, what is the net yield of ATP from this pathway? (For this question, ignore what could be obtained if the acetyl-CoA enters the TCA cycle. Consider the pathway only up to acetylCoA.) A. 28 moles of ATP per mole of fatty acid oxidized B. 30 moles of ATP per mole of fatty acid oxidized C. 32 moles of ATP per mole of fatty acid oxidized D. 106 moles of ATP per mole of fatty acid oxidized 3. Which of these molecules is an intermediate in the synthesis of ketone bodies from acetyl-CoA? A. B. C. D. all of the above 4. Which of the following coenzymes is required in the synthesis of ketone bodies from acetyl-CoA? A. biotin B. coenzyme B12 C. pyridoxal phosphate D. none of the above 5. Which of the following is part of the pathway in which a fatty acid with an odd number of carbon atoms is oxidized? A. B. C. D. all of the above name ______________________________________ 6. The overal rate of fatty acid oxidation is determined by the rate of the reaction catalyzed by: A. carnitine acyltransferase I B. acyl-CoA synthetase C. acyl-CoA dehydrogenase D. thiolase 7. In addition to the unsaturated fatty-acly-CoA, the reaction catalyzed by stearoyl-CoA desaturase generates: A. NADH and O2 B. NADH and H2O C. NAD+ and O2 D. NAD+ and H2O 8. Which of the following enzymes has cytosolic acetyl-CoA as one of its products? A. malic enzyme B. pyruvate dehydrogenase C. carnitine acyltransferase I D. ATP-citrate lyase 9. The reaction catalyzed by malic enzyme generates: A. malonyl-CoA. B. pyruvate and NADPH. C. malate from oxaloacetate. D. ADP from ATP. 10. Fatty acids are exported from the liver as triacylglycerol in the core of: A. chylomicrons. B. LDL. C. VLDL. D. all of the above 11. Receptor-mediated endocytosis is the process by which: A. insulin enters cells. B. LDL is taken up by cells. C. VLDL is taken up by cells. D. all of the above 12. In the reaction catalyzed by nitrogenase: A. electrons are supplied by H2. B. 8 moles of ATP are required for each mole of N2 reduced. C. N2 is converted to NH4+. D. all of the above 13. Catabolism of the amino acid valine generates succinyl-CoA. Valine is therefore: A. glucogenic B. ketogenic C. both ketogenic and glucogenic D. essential 14. Acetyl-CoA labeled with 14C in the number 2 carbon (the methyl group of acetate) is used in fatty acid synthesis catalyzed by acetyl-CoA carboxylase and fatty acid synthase. After synthesis of a fatty acid containing 16 carbon atoms, which carbons in the fatty acid will contain label? A. only carbon number 16 (the carbon farthest from the carboxylic acid) B. all the even-numbered carbons C. all the odd-numbered carbons D. Not enough information is given to answer. 15. Which of the following is a product of a transaminase reaction between aspartate and α-ketoglutarate? A. pyruvate B. fumarate C. glutamine D. oxaloacetate 2 name ______________________________________ Questions 16-22. Write your answers in the space provided. PLEASE READ THIS. In some of the following questions you are asked to draw metabolic reactions and show structures of reactants and products. In your answers you do not need to draw the structures of ATP, NAD(P)+, NAD(P)H, CoA, or any coenzyme required in the reaction. However, please clearly show the steps where these molecules are utilized. 16 (20 pts). Palmitate (a saturated fatty acid with 16 carbons) is the primary product of fatty acid synthase. Saturated fatty acids with much longer chains can be synthesized starting from palmitate via special elongation reactions, which occur on the outer face of the endoplasmic reticulum. These elongation reactions are exactly analogous to the reactions catalyzed by fatty acid synthase, except that each enzyme activity is present on a separate protein and the intermediates are all bound to Coenzyme A (not acyl carrier protein). For example, the elongation reaction catalyzed by β-ketoacyl CoA synthase would (in the first cycle of elongation) use palmitoyl-CoA and malonyl-CoA as substrates to generate β-ketoacyl-CoA. Starting with palmitate, the free fatty acid product of fatty acid synthase, show the steps in this elongation pathway to generate stearoylCoA. (Stearic acid is a saturated fatty acid with 18 carbons.) Show the structures and general names for all reactants and products and the name of each enzyme. 3 name ______________________________________ 17 (12 pts). Starting with acetyl-CoA, draw the pathway of cholesterol synthesis through the step catalyzed by HMG-CoA reductase. Show the names and structures of all reactants and products and the names of enzymes. 18 (8 pts). Draw the mechanism of the rate-determining reaction in fatty acid synthesis. Name the enzyme that catalyzes this reaction. A structure you may find useful is shown below. 19 (5 pts). Draw the reaction that is rate-determining in fatty acid oxidation. Show the names and structures of all reactants and products and name the enzyme. 4 name ______________________________________ 20 (15 pts). Starting with carbamoyl-phosphate and ornithine, draw the reactions of the urea cycle. Show the names and structures of all reactants and products and the names of enzymes. Show the cellular compartment in which each reaction occurs. 5 name ______________________________________ 21 (10 pts). The structure shown below is a Schiff base formed by pyridoxal phosphate and the amino acid tyrosine during a transaminase reaction. Show the mechanism the transaminase uses to convert this molecule to an α-keto acid and the pyridoxamine form of pyridoxal phosphate. 6 ...
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