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Sample Problem 24.1 Fats and Digestion Answer each of the following for the digestion of triacylglycerols: a Where does it take place? b What enzyme is involved? c What are the products of digestion? Solution a the small intestine b pancreatic lipase c monoacylglycerols and fatty acids Study Check 24.1 How are the nonpolar triacylglycerols emulsified so that they can be digested? Answer The triacylglycerols entering the small intestine are emulsified by bile salts into smaller droplets of fat that can react with the lipases General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.2 β Oxidation Match each of the following (a to d) with one of the reactions (1 to 4) in the β oxidation cycle: (1) first oxidation (2) hydration (3) second oxidation (4) cleavage (thiolysis) a Water is added to a trans double bond b An acetyl CoA is removed c FAD is reduced to FADH2 d A 3-hydroxyacyl CoA is converted to 3-ketoacyl CoA Solution a (2) hydration b d (3) second oxidation (4) cleavage (thiolysis) c (1) first oxidation Study Check 24.2 Determine the number of β oxidation cycles and number of acetyl CoA molecules produced for cerotic acid (C26), a fatty acid found in beeswax and carnauba wax Answer Cerotic acid (C26) requires 12 β oxidation cycles, and produces 13 acetyl CoA molecules General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.3 ATP Production from β Oxidation How many ATP will be produced from the β oxidation of palmitic acid, a C16 saturated fatty acid? Solution Palmitic acid (C16) requires seven β oxidation cycles, which produce seven NADH and seven FADH2 The total number of acetyl CoA is eight The activation of palmitic acid decreases the total produced by two ATP Study Check 24.3 Compare the total ATP from the reduced coenzymes and from acetyl CoA in the β oxidation of palmitic acid General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.3 ATP Production from β Oxidation Continued Answer Eight acetyl CoA units yield 80 ATP whereas seven NADH and seven FADH2 yield 28 ATP General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.4 Ketogenesis The process called ketogenesis takes place in the liver a What are some conditions that promote ketogenesis? b What are the names of the three compounds called ketone bodies? c What ketone bodies are responsible for the acidosis that occurs in ketogenesis? Solution a When excess acetyl CoA cannot be processed by the citric acid cycle, acetyl CoA molecules enter the ketogenesis pathway and form ketone bodies b The ketone bodies are acetoacetate, β-hydroxybutyrate, and acetone c The ketone bodies acetoacetate and β-hydroxybutyrate, which are carboxylic acids, can decrease the pH of the blood (metabolic acidosis) Study Check 24.4 Which ketone bodies contain each of the following functional groups? a ketone b alcohol Answer a Acetone contains a ketone group b β-Hydroxybutyrate contains an alcohol group General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.5 Fatty Acid Synthesis Malonyl ACP is required for the elongation of fatty acid chains a Complete the following equations for the formation of malonyl ACP from the starting material: Acetyl CoA + HCO3− + ATP → Malonyl CoA + HS—ACP → b What enzymes catalyze these reactions? Solution a Acetyl CoA combines with bicarbonate to form malonyl CoA, which reacts with ACP to form malonyl ACP Acetyl CoA + HCO3− + ATP → malonyl CoA + ADP + Pi + H+ Malonyl CoA + HS—ACP → malonyl ACP + HS—CoA b The enzyme for the first reaction is acetyl CoA carboxylase The enzyme for the second reaction is malonyl CoA transacylase Study Check 24.5 If malonyl ACP is a three-carbon acyl group, why are only two carbon atoms added each time malonyl ACP is combined with a fatty acid chain? Answer In each cycle of fatty acid synthesis, a two-carbon acetyl group from the three-carbon group in malonyl ACP adds to the growing fatty acid chain and one carbon forms CO2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.6 Digestion of Proteins What are the sites and end products for the digestion of proteins? Solution The digestion of proteins begins in the stomach and is completed in the small intestine to yield amino acids Study Check 24.6 What is the function of HCl in the stomach? Answer HCl denatures proteins and activates enzymes such as pepsin General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.7 Nitrogen Balance With a positive nitrogen balance, why are excess amino acids excreted? Solution Because the body cannot store nitrogen, amino acids that are not needed for the synthesis of proteins are excreted Study Check 24.7 Under what condition does the body have a negative nitrogen balance? Answer In conditions such as fasting or starvation, a diet insufficient in protein leads to a negative nitrogen balance General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.8 Transamination Write the equation for the transamination of glutamate and oxaloacetate by drawing the condensed structural formulas Solution Study Check 24.8 What are some other possible names for the enzyme that catalyzes the reaction in Sample Problem 24.8? Answer glutamate aminotransferase, glutamate transaminase, aspartate aminotransferase General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.9 Transamination and Oxidative Deamination Indicate whether each of the following represents a transamination or an oxidative deamination: a Glutamate is converted to α-ketoglutarate and NH4+ b Alanine and α-ketoglutarate react to form pyruvate and glutamate Solution a Oxidative deamination occurs when the —NH3+ group in glutamate is removed as an ammonium ion, NH4+ b Transamination occurs when an amino group is transferred from an amino acid to an α-keto acid such as α-ketoglutarate Study Check 24.9 Is the reaction catalyzed by glutamate dehydrogenase, which requires NAD +, an example of transamination or oxidative deamination? Answer oxidative deamination General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Sample Problem 24.10 Urea Cycle Indicate the reaction in the urea cycle where each of the following compounds is a reactant: a aspartate b ornithine c arginine Solution a Aspartate and citrulline undergo condensation in reaction b A carbamoyl group is transferred to ornithine in reaction c Arginine is cleaved in reaction Study Check 24.10 Name the products of each reaction in Sample Problem 24.10 Answer a argininosuccinat b citrulline c General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake urea and ornithine © 2016 Pearson Education, Inc Sample Problem 24.11 Degradation of Amino Acids Identify the citric acid cycle component and the number of ATP produced by each of the following amino acids: a proline b tyrosine c tryptophan Solution a Proline is converted to the citric acid cycle intermediate α-ketoglutarate The reactions in the remaining part of the citric acid cycle from α-ketoglutarate to oxaloacetate produce two NADH, one GTP, and one FADH2 The two NADH provide five ATP, one GTP provides one ATP, and one FADH2 provides 1.5 ATP, for a total of 7.5 ATP from proline b Tyrosine is converted to the citric acid cycle intermediate fumarate The remaining reactions of the citric acid cycle from fumarate to oxaloacetate produce one NADH, which provides 2.5 ATP c Tryptophan is converted to the citric acid cycle intermediate acetyl CoA The reactions in the citric acid cycle starting with acetyl CoA produce three NADH, one GTP, and one FADH2 The three NADH provide 7.5 ATP, one GTP provides one ATP, and one FADH2 provides 1.5 ATP, for a total of 10 ATP from tryptophan Study Check 24.11 Why does the citric acid cycle component from leucine supply more ATP than the intermediate from phenylalanine? Answer Leucine forms the citric acid cycle intermediate acetyl CoA that enters at the beginning of the citric acid cycle to provide 10 ATP Phenylalanine forms the citric acid cycle intermediate fumarate that enters later in the citric acid cycle to produce one NADH, which is used to provide 2.5 ATP General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc ... total ATP from the reduced coenzymes and from acetyl CoA in the β oxidation of palmitic acid General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson... acetyl CoA units yield 80 ATP whereas seven NADH and seven FADH2 yield 28 ATP General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc... malonyl ACP adds to the growing fatty acid chain and one carbon forms CO2 General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc
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