Introduction to Metabolism

If the ΔG'° of the reaction A → B is –40 kJ/mol, under standard conditions the reaction: A) is at equilibrium. B) will never reach equilibrium. C) will not occur spontaneously. D) will proceed at a rapid rate. E) will proceed spontaneously from left to right.

For the reaction A → B, ΔG'° = –60 kJ/mol. The reaction is started with 10 mmol of A; no B is initially present. After 24 hours, analysis reveals the presence of 2 mmol of B, 8 mmol of A. Which is the most likely explanation? A) A and B have reached equilibrium concentrations. B) An enzyme has shifted the equilibrium toward A. C) B formation is kinetically slow; equilibrium has not been reached by 24 hours. D) Formation of B is thermodynamically unfavorable. E) The result described is impossible, given the fact that ΔG'° is –60 kJ/mol.

When a mixture of 3-phosphoglycerate and 2-phosphoglycerate is incubated at 25°C with phosphoglycerate mutase until equilibrium is reached, the final mixture contains six times as much 2-phosphoglycerate as 3-phosphoglycerate. Which one of the following statements is most nearly correct, when applied to the reaction as written? (R = 8.315 J/mol·K; T = 298 K)

3-Phosphoglycerate → 2-phosphoglycerate

A) ΔG'° is –4.44 kJ/mol. B) ΔG'° is zero. C) ΔG'° is +12.7 kJ/mol. D) ΔG'° is incalculably large and positive. E) ΔG'° cannot be calculated from the information given.

When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme phosphohexose isomerase (which catalyzes the interconversion of these two compounds) until equilibrium is reached, the final mixture contains twice as much glucose 6-phosphate as fructose 6-phosphate. Which one of the following statements is best applied to this reaction outlined below?

(R = 8.315 J/mol·K; T = 298 K) Glucose 6-phosphate → fructose 6-phosphate

A) ΔG'° is incalculably large and negative. B) ΔG'° is –1.72 kJ/mol. C) ΔG'° is zero. D) ΔG'° is +1.72 kJ/mol. E) ΔG'° is incalculably large and positive.

The reaction ATP ADP + Pi is an example of a(n) reaction. A) homolytic cleavage B) internal rearrangement C) free radical D) group transfer E) oxidation/reduction

All of the following contribute to the large, negative, free-energy change upon hydrolysis of “high-energy” compounds except: A) electrostatic repulsion in the reactant. B) low activation energy of forward reaction. C) stabilization of products by extra resonance forms. D) stabilization of products by ionization. E) stabilization of products by solvation.

The hydrolysis of ATP has a large negative ΔG'°; nevertheless it is stable in solution due to: A) entropy stabilization. B) ionization of the phosphates. C) resonance stabilization. D) the hydrolysis reaction being endergonic. E) the hydrolysis reaction having a large activation energy.

The hydrolysis of phosphoenolpyruvate proceeds with a ΔG'° of about –62 kJ/mol. The greatest contributing factors to this reaction are the destabilization of the reactants by electrostatic repulsion and stabilization of the product pyruvate by: A) electrostatic attraction. B) ionization. C) polarization. D) resonance. E) tautomerization.

Biological oxidation-reduction reactions never involve: A) transfer of e- from one molecule to another. B) formation of free e-. C) transfer of H+ (or H3O+) from one molecule to another. D) formation of free H+ (or H3O+). E) None of the above.

The structure of NAD

+ does not include:

A) a flavin nucleotide. B) a pyrophosphate bond. C) an adenine nucleotide. D) nicotinamide. E) two ribose residues.

Short Answer Questions

Consider the reaction: A + B → C + D. If the equilibrium constant for this reaction is a large number (say, 10,000), what do we get/know about the standard free-energy change (ΔG'°) for the reaction? Describe the relationship between Keq' and ΔG'°.

What is the difference between ΔG and ΔG'° of a chemical reaction? Describe, quantitatively, the relationship between them.

Classify each of the *-marked atoms as an electrophile or an nucleophile:

(a) (b) (c) (d) (e)

H O

N

CH3

CH3

CH3

O

N

*

*

*

**

Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway Glycolysis is the name given to a metabolic pathway occurring in many different cell types. When it consists of 11 enzymatic steps it converts glucose to lactic acid. It is an example of: A) aerobic metabolism. B) anabolic metabolism. C) a net reductive process. D) anaerobic metabolism. E) oxidative phosphorylation. The anaerobic conversion of 1 mol of glucose to 2 mol of lactate by fermentation is accompanied by a net gain of: A) 1 mol of ATP. B) 1 mol of NADH. C) 2 mol of ATP. D) 2 mol of NADH. E) none of the above. The conversion of 1 mol of fructose 1,6-bisphosphate to 2 mol of pyruvate by the glycolytic pathway results in a net formation of: A) 1 mol of NAD+ and 2 mol of ATP. B) 1 mol of NADH and 1 mol of ATP. C) 2 mol of NAD+ and 4 mol of ATP. D) 2 mol of NADH and 2 mol of ATP. E) 2 mol of NADH and 4 mol of ATP. Which of the following statements is not true concerning glycolysis in anaerobic muscle? A) Fructose 1,6-bisphosphatase is one of the enzymes of the pathway. B) It is an endergonic process. C) It results in net synthesis of ATP. D) It results in synthesis of NADH. E) Its rate is slowed by a high [ATP]/[ADP] ratio. When a muscle is stimulated to contract aerobically, less lactic acid is formed than when it contracts anaerobically because: A) glycolysis does not occur to significant extent under aerobic conditions. B) muscle is metabolically less active under aerobic than anaerobic conditions. C) the lactic acid generated is rapidly incorporated into lipids under aerobic conditions. D) under aerobic conditions in muscle, the major energy-yielding pathway is the pentose phosphate pathway, which does not produce lactate. E) under aerobic conditions, most of the pyruvate generated as a result of glycolysis is oxidized by the citric acid cycle rather than reduced to lactate. Glycolysis in the erythrocyte produces pyruvate that is further metabolized to: A) CO2. B) ethanol. C) glucose. D) hemoglobin. E) lactate.

Which of these cofactors participates directly in most of the oxidation-reduction reactions in the fermentation of glucose to lactate? A) ADP B) ATP C) FAD/FADH2 D) Glyceraldehyde 3-phosphate E) NAD+/NADH In comparison with the resting state, actively contracting human muscle tissue has a: A) higher concentration of ATP. B) higher rate of lactate formation. C) lower consumption of glucose. D) lower rate of consumption of oxygen E) lower ratio of NADH to NAD+. The steps of glycolysis between glyceraldehyde 3-phosphate and 3-phosphoglycerate involve all of the following except: A) ATP synthesis. B) catalysis by phosphoglycerate kinase. C) oxidation of NADH to NAD+. D) the formation of 1,3-bisphosphoglycerate. E) utilization of Pi. The first reaction in glycolysis that results in the formation of an energy-rich compound (in other words, a compound whose hydrolysis has a highly negative ΔG'°) is catalyzed by: A) glyceraldehyde 3-phosphate dehydrogenase. B) hexokinase. C) phosphofructokinase-1. D) phosphoglycerate kinase. E) triose phosphate isomerase. Which of the following statements is incorrect? A) Aerobically, oxidative decarboxylation of pyruvate forms acetate that enters the citric acid cycle. B) In anaerobic muscle, pyruvate is converted to lactate. C) In yeast growing anaerobically, pyruvate is converted to ethanol. D) Reduction of pyruvate to lactate regenerates a cofactor essential for glycolysis. E) Under anaerobic conditions, pyruvate does not form because glycolysis does not occur. The ultimate electron acceptor in the fermentation of glucose to ethanol is: A) acetaldehyde. B) acetate. C) ethanol. D) NAD+. E) pyruvate.

Which of the following compounds cannot serve as the starting material for the synthesis of glucose via gluconeogenesis? A) acetate B) glycerol C) lactate D) oxaloacetate E) α-ketoglutarate Which one of the following statements about gluconeogenesis is false? A) For starting materials, it can use carbon skeletons derived from certain amino acids. B) It consists entirely of the reactions of glycolysis, operating in the reverse direction. C) It employs the enzyme glucose 6-phosphatase. D) It is one of the ways that mammals maintain normal blood glucose levels between meals. E) It requires metabolic energy (ATP or GTP). In humans, gluconeogenesis: A) can result in the conversion of protein into blood glucose. B) helps to reduce blood glucose after a carbohydrate-rich meal. C) is activated by the hormone insulin D) is essential in the conversion of fatty acids to glucose. E) requires the enzyme hexokinase. Which of the following substrates cannot contribute to net gluconeogenesis in mammalian liver? A) alanine B) glutamate C) palmitate D) pyruvate E) α-ketoglutarate Which of the following statements about the pentose phosphate pathway is correct? A) It generates 36 mol of ATP per mole of glucose consumed. B) It generates 6 moles of CO2 for each mole of glucose consumed. C) It is a reductive pathway; it consumes NADH. D) It is present in plants, but not in animals. E) It provides precursors for the synthesis of nucleotides. The main function of the pentose phosphate pathway is to: A) give the cell an alternative pathway should glycolysis fail. B) provide a mechanism for the utilization of the carbon skeletons of excess amino acids. C) supply energy. D) supply NADH. E) supply pentoses and NADPH. The metabolic function of the pentose phosphate pathway is to: A) act as a source of ADP biosynthesis. B) generate NADPH and pentoses for the biosynthesis of fatty acids and nucleic acids. C) participate in oxidation-reduction reactions during the formation of H2O. D) provide intermediates for the citric acid cycle. E) synthesize phosphorus pentoxide.

Which of the following statements about the pentose phosphate pathway is incorrect? A) It generates CO2 from C-1 of glucose. B) It involves the conversion of an aldohexose to an aldopentose. C) It is prominent in lactating mammary glands. D) It is principally directed toward the generation of NADPH. E) It requires the participation of molecular oxygen. Glucose breakdown in certain mammalian and bacterial cells can occur by mechanisms other than classic glycolysis. In most of these, glucose 6-phosphate is oxidized to 6-phosphogluconate, which is then further metabolized by: A) an aldolase-type split to form glyceric acid and glyceraldehyde 3-phosphate. B) an aldolase-type split to form glycolic acid and erythrose 4-phosphate. C) conversion to 1,6-bisphosphogluconate. D) decarboxylation to produce keto- and aldopentoses. E) oxidation to a six-carbon dicarboxylic acid. Which of the following enzymes acts in the pentose phosphate pathway? A) 6-phosphogluconate dehydrogenase B) Aldolase C) Glycogen phosphorylase D) Phosphofructokinase-1 E) Pyruvate kinase The oxidation of 3 mol of glucose by the pentose phosphate pathway may result in the production of: A) 2 mol of pentose, 4 mol of NADPH, and 8 mol of CO2. B) 3 mol of pentose, 4 mol of NADPH, and 3 mol of CO2. C) 3 mol of pentose, 6 mol of NADPH, and 3 mol of CO2. D) 4 mol of pentose, 3 mol of NADPH, and 3 mol of CO2. E) 4 mol of pentose, 6 mol of NADPH, and 6 mol of CO2. In a tissue that metabolizes glucose via the pentose phosphate pathway, C-1 of glucose would be expected to end up principally in: A) carbon dioxide. B) glycogen. C) phosphoglycerate. D) pyruvate. E) ribulose 5-phosphate. Short Answer Questions In glycolysis there are two reactions that require one ATP each and two reactions that produce one ATP each. How can glycolysis lead to the net production of two ATP molecules per glucose? Briefly describe the possible metabolic fates (there are more than one) of pyruvate produced by glycolysis in humans, and explain the circumstances that favor each.

The yeast used in brewing the alcoholic beverage beer can break down glucose either aerobically or anaerobically. Explain why beer is brewed under anaerobic conditions. All of the intermediated in the glycolytic pathway are phosphorylated. Give two reasons why this might be advantageous to the cell. Describe the part preparatory pathway of glycolysis showing structures of intermediates, enzyme names, and indicate where cofactors participate. Describe the part pay-off pathway of glycolysis showing structures of intermediates, enzyme names, and indicate where cofactors participate. Rat liver is able to metabolize glucose by both the glycolytic and the pentose phosphate pathways. Indicate in the blanks if the following are properties of glycolytic (G), pentose phosphate (P), both (G + P), or neither (0): _____ NAD+ is involved. _____ CO2 is liberated. _____ Phosphate esters are intermediates. _____ Glyceraldehyde 3-phosphate is an intermediate. _____ Fructose 6-phosphate is an intermediate. At which point in glycolysis do C-3 and C-4 of glucose become chemically equivalent? What is gluconeogenesis, and what useful purposes does it serve in people? What are the biological functions of the pentose phosphate pathway?

The Citric Acid Cycle

Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl-CoA? A) ATP B) CoA-SH C) FAD D) Lipoic acid E) NAD+ Which combination of cofactors is involved in the conversion of pyruvate to acetyl-CoA? A) Biotin, FAD, and TPP B) Biotin, NAD+, and FAD C) NAD+, biotin, and TPP D) Pyridoxal phosphate, FAD, and lipoic acid E) TPP, lipoic acid, and NAD+ Which of the following is not an intermediate of the citric acid cycle? A) Acetyl-CoA B) Citrate C) Oxaloacetate D) Succinyl-CoA E) α-Ketoglutarate

In mammals, each of the following occurs during the citric acid cycle except: A) formation of α-ketoglutarate. B) generation of NADH and FADH2. C) metabolism of acetate to carbon dioxide and water. D) net synthesis of oxaloacetate from acetyl-CoA. E) oxidation of acetyl-CoA.

Conversion of 1 mol of acetyl-CoA to 2 mol of CO2 and CoA via the citric acid cycle results in the net production of: A) 1 mol of citrate. B) 1 mol of FADH2. C) 1 mol of NADH. D) 1 mol of oxaloacetate. E) 7 mol of ATP.

The oxidative decarboxylation of α-ketoglutarate proceeds by means of multistep reactions. Which of the following cofactors is not required in this reaction? A) ATP B) Coenzyme A C) Lipoic acid D) NAD+ E) Thiamine pyrophosphate

The reaction of the citric acid cycle that is most similar to the pyruvate dehydrogenase complex-catalyzed conversion of pyruvate to acetyl-CoA is the conversion of: A) citrate to isocitrate. B) fumarate to malate. C) malate to oxaloacetate. D) succinyl-CoA to succinate. E) α-ketoglutarate to succinyl-CoA.

The reaction of the citric acid cycle that produces an ATP equivalent (in the form of GTP) by substrate level phosphorylation is the conversion of: A) citrate to isocitrate. B) fumarate to malate. C) malate to oxaloacetate. D) succinate to fumarate. E) succinyl-CoA to succinate.

All of the oxidative steps of the citric acid cycle are linked to the reduction of NAD

+ except the

reaction catalyzed by: A) isocitrate dehydrogenase. B) malate dehydrogenase. C) pyruvate dehydrogenase. D) succinate dehydrogenase. E) the α-ketoglutarate dehydrogenase complex.

Which of the following cofactors is required for the conversion of succinate to fumarate in the citric acid cycle? A) ATP B) Biotin C) FAD D) NAD+ E) NADP+

In the citric acid cycle, a flavin coenzyme is required for: A) condensation of acetyl-CoA and oxaloacetate. B) oxidation of fumarate. C) oxidation of isocitrate. D) oxidation of malate. E) oxidation of succinate.

Anaplerotic reactions . A) produce oxaloacetate and malate to maintain constant levels of citric acid cycle intermediates. B) produce biotin needed by pyruvate carboxylase. C) recycle pantothenate used to make CoA. D) produce pyruvate and citrate to maintain constant levels of citric acid cycle intermediates. E) All of the above.

The conversion of 1 mol of pyruvate to 3 mol of CO2 via pyruvate dehydrogenase and the citric acid cycle also yields _____ mol of NADH, _____ mol of FADH2, and _____ mol of ATP (or GTP). A) 2; 2; 2 B) 3; 1; 1 C) 3; 2; 0 D) 4; 1; 1 E) 4; 2; 1 During seed germination, the glyoxylate pathway is important to plants because it enables them: A) carry out the net synthesis of glucose from acetyl-CoA. B) form acetyl-CoA from malate. C) get rid of isocitrate formed from the aconitase reaction. D) obtain glyoxylate for cholesterol biosynthesis. E) obtain glyoxylate for pyrimidine synthesis. The glyoxylate cycle is: A) a means of using acetate for both energy and biosynthetic precursors. B) an alternative path of glucose metabolism in cells that do not have enough O2. C) defective in people with phenylketonuria. D) is not active in a mammalian liver. E) the most direct way of providing the precursors for synthesis of nucleic acids (for example,

ribose). Short Answer Questions

The citric acid cycle begins with the condensation of acetyl-CoA with oxaloacetate. Describe at least two of three possible sources for the acetyl-CoA.

Briefly describe the relationship of the pyruvate dehydrogenase complex reaction to glycolysis and the citric acid cycle. What is the function of FAD in the pyruvate dehydrogenase complex? How is it regenerated?

Match the cofactors below with their roles in the pyruvate dehydrogenase complex reaction: Cofactors: A. Coenzyme A (CoA-SH) B. NAD+ C. Thiamine pyrophosphate (TPP) D. FAD E. Lipoic acid in oxidized form Roles: _______ Attacks and attaches to the central carbon in pyruvate. _______ Oxidizes FADH2. _______ Accepts the acetyl group from reduced lipoic acid. _______ Oxidizes the reduced form of lipoic acid. _______ Initial electron acceptor in oxidation of pyruvate. Draw the citric acid cycle from isocitrate to fumarate only, showing and naming each intermediate. Show where high-energy phosphate compounds or reduced electron carriers are produced or consumed, and name the enzyme that catalyzes each step. Show the reactions by which α-ketoglutarate is converted to malate in the citric acid cycle. Show the steps of the citric acid cycle in which a six-carbon compound is converted into the first four-carbon intermediate in the path. For each step, show structures of substrate and product, name the enzyme responsible. Show the steps of the citric acid cycle from oxaloacetate to succinyl-CoA only. For each step, show structures of substrate and product, name the enzyme responsible, and show where cofactors participate.

In the citric acid cycle, a five-carbon compound is decarboxylated to yield an activated four-carbon compound. Draw the reaction with proper formulas of substrate, product. In which reaction of the citric acid cycle does substrate-level phosphorylation occur? Draw the reaction with proper formulas.

Oxidative Phosphorylation and Photophosphorylation

Almost all of the oxygen (O2) one consumes in breathing is converted to: A) acetyl-CoA. B) carbon dioxide (CO2). C) carbon monoxide and then to carbon dioxide. D) none of the above. E) water.

Antimycin A blocks electron transfer between cytochromes b and c1. If intact mitochondria were incubated with antimycin A in an excess of NADH and an adequate supply of O2, which of the following compounds would be found in the oxidized state? A) Coenzyme Q B) Cytochrome a3 C) Cytochrome b D) Cytochrome e E) Cytochrome f

In the reoxidation of QH2 by purified ubiquinone-cytochrome c reductase (Complex III) from heart muscle, the overall stoichiometry of the reaction requires 2 mol of cytochrome c per mole of QH2 because: A) cytochrome c is a one-electron acceptor, whereas QH2 is a two-electron donor. B) cytochrome c is a two-electron acceptor, whereas QH2 is a one-electron donor. C) cytochrome c is water soluble and operates between the inner and outer mitochondrial

membranes D) heart muscle has a high rate of oxidative metabolism, and therefore requires twice as much

cytochrome c as QH2 for electron transfer to proceed normally. E) two molecules of cytochrome c must first combine physically before they are catalytically active.

If electron transfer in mitochondria is blocked (with antimycin A) between cytochrome b and cytochrome c1, then: A) all ATP synthesis will stop. B) ATP synthesis will continue, but the P/O ratio will drop to one. C) electron transfer from NADH will cease, but O2 uptake will continue. D) electron transfer from succinate to O2 will continue unabated. E) energy diverted from the cytochromes will be used to make ATP, and the P/O ratio will rise.

Which of the following statements about the chemiosmotic theory is correct? A) Electron transfer in mitochondria is accompanied by an asymmetric release of protons on one

side of the inner mitochondrial membrane. B) It predicts that oxidative phosphorylation can occur even in the absence of an intact inner

mitochondrial membrance. C) The effect of inhibitors is a consequence of their ability to carry electrons through membranes. D) The membrane ATP synthase has no significant role in the chemiosmotic theory. E) All of the above are correct.

Oxidative phosphorylation and photophosphorylation share all of the following except: A) chlorophyll. B) involvement of cytochromes. C) participation of quinones. D) proton pumping across a membrane to create electrochemical potential. E) use of iron-sulfur proteins.

Short Answer Questions

As you read and answer this question, you are (presumably) consuming oxygen. What is the reaction that consumes most of your oxygen and where would you locate it?

Two compounds of mitochondrial respiratory chain Q and O2 has a standard reduction potential (E'°) of 0.82 V and 0.045 V. Which value belongs to each compound and why do you think so?

Diagram the path of electron flow from NADH to the final electron acceptor during electron transport in mitochondria. Name each electron carrier, indicate whether only electrons, or both electrons and protons, are accepted/donated by that carrier. Diagram the path of electron flow from FADH2 to the final electron acceptor during electron transport in mitochondria. Name each electron carrier, indicate whether only electrons, or both electrons and protons, are accepted/donated by that carrier.

Fatty Acid Metabolism

Lipoprotein lipase acts in: A) hydrolysis of triacylglycerols of plasma lipoproteins to supply fatty acids to various tissues. B) intestinal uptake of dietary fat. C) intracellular lipid breakdown of lipoproteins. D) lipoprotein breakdown to supply needed amino acids. E) none of the above.

Free fatty acids in the bloodstream are: A) bound to hemoglobin. B) carried by the protein serum albumin. C) freely soluble in the aqueous phase of the blood. D) nonexistent; the blood does not contain free fatty acids. E) present at levels that are independent of epinephrine.

The glycerol produced from the hydrolysis of triacylglycerides enters glycolysis as: A) glucose. B) glucose-6-phosphate. C) glyceraldehyde 3-phosphate. D) pyruvate. E) glyceryl CoA.

Transport of fatty acids from the cytoplasm to the mitochondrial matrix requires: A) ATP, carnitine, and coenzyme A. B) ATP, carnitine, and pyruvate dehydrogenase. C) ATP, coenzyme A, and hexokinase. D) ATP, coenzyme A, and pyruvate dehydrogenase. E) carnitine, coenzyme A, and hexokinase.

Fatty acids are activated to acyl-CoAs, the acyl group is further transferred to carnitine because: A) acyl-carnitines can cross the mitochondrial inner membrane, but acyl-CoAs do not. B) acyl-CoAs easily cross the mitochondrial membrane, but the fatty acids themselves will not. C) carnitine is required to oxidize NAD

+ to NADH.

D) fatty acids cannot be oxidized by FAD unless they are in the acyl-carnitine form. E) None of the above is true. Carnitine is: A) a 15-carbon fatty acid. B) an essential cofactor for the citric acid cycle. C) essential for intracellular transport of fatty acids. D) one of the amino acids commonly found in protein. E) present only in carnivorous animals.

Which of these is able to cross the inner mitochondrial membrane? A) Acetyl–CoA B) Fatty acyl–carnitine C) Fatty acyl–CoA D) Malonyl–CoA E) None of the above can cross.

What is the correct order of function of the following enzymes of β oxidation?

1. β-Hydroxyacyl-CoA dehydrogenase 2. Thiolase 3. Enoyl-CoA hydratase 4. Acyl-CoA dehydrogenase

A) 1, 2, 3, 4 B) 3, 1, 4, 2 C) 4, 3, 1, 2 D) 1, 4, 3, 2 E) 4, 2, 3, 1

If the 16-carbon saturated fatty acid palmitate is oxidized completely to carbon dioxide and water (via the β-oxidation pathway and the citric acid cycle), and all of the energy-conserving products are used to drive ATP synthesis in the mitochondrion, the net yield of ATP per molecule of palmitate is: A) 3. B) 10. C) 25. D) 108. E) 1,000.

Complete oxidation of 1 mole of which fatty acid would yield the most ATP? A) 16-carbon saturated fatty acid B) 18-carbon mono-unsaturated fatty acid C) 16-carbon mono-unsaturated fatty acid D) 16-carbon poly-unsaturated fatty acid E) 14-carbon saturated fatty acid

Which of the following statements concerning the β oxidation of fatty acids is true? A) About 1,200 ATP molecules are ultimately produced per 20-carbon fatty acid oxidized. B) One FADH2 and two NADH are produced for each acetyl-CoA. C) The free fatty acid must be carboxylated in the β position by a biotin-dependent reaction before

the process of β oxidation commences. D) The free fatty acid must be converted to a thioester before the process of β oxidation starts. E) Two NADH are produced for each acetyl-CoA.

Which compound is an intermediate of the β oxidation of fatty acids? A) CH3—(CH2)20—CO—COOH B) CH3—CH2—CO—CH2—CO—OPO3

2– C) CH3—CH2—CO—CH2—OH D) CH3—CH2—CO—CO—S—CoA E) CH3—CO—CH2—CO—S—CoA

The conversion of palmitoyl-CoA (16:0) to myristoyl-CoA (14:0) and 1 mol of acetyl-CoA by the β-oxidation pathway results in the net formation of: A) 1 FADH2 and 1 NADH. B) 1 FADH2 and 1 NADPH. C) 1 FADH2, 1 NADH, and 1 ATP. D) 2 FADH2 and 2 NADH. E) 2 FADH2, 2 NADH, and 1 ATP.

If an aerobic organism were fed with each of the following three compounds as a source of energy, the energy yield per mole from these molecules would be in the order: A) alanine > glucose > palmitate (16:0). B) glucose > alanine > palmitate. C) glucose > palmitate > alanine. D) palmitate > alanine > glucose. E) palmitate > glucose > alanine.

Ketone bodies are formed in the liver and transported to the extrahepatic tissues mainly as: A) acetoacetyl-CoA. B) acetone. C) beta-hydroxybutyric acid. D) beta-hydroxybutyryl-CoA. E) lactic acid. The major site of formation of acetoacetate from fatty acids is the: A) adipose tissue. B) intestinal mucosa. C) kidney. D) liver. E) muscle.

Which of the following is not required in the synthesis of fatty acids? A) Acetyl-CoA B) Biotin C) HCO3

– (CO2)

D) Malonyl-CoA E) NADH

Which of the following is not true of the reaction producing malonyl-CoA during fatty acid synthesis? A) It is stimulated by citrate. B) It requires acyl carrier protein (ACP). C) It requires CO2 (or bicarbonate). D) One mole of ATP is converted to ADP + Pi for each malonyl-CoA synthesized. E) The cofactor is biotin.

Which of the following is not true of the fatty acid synthase and the fatty acid β-oxidation systems? A) A derivative of the vitamin pantothenic acid is involved. B) Acyl-CoA derivatives are intermediates. C) Double bonds are oxidized or reduced by pyridine nucleotide coenzymes. D) The processes occur in different cellular compartments. E) The processes occur in the mitochondrial matrix.

Which of these can be synthesized by plants but not by humans? A) Linoleate [18:2(Δ

9,12)]

B) Palmitate (16:0) C) Phosphatidylcholine D) Pyruvate E) Stearate (18:0)

Short Answer Questions

The oxidation of acetyl-CoA added to isolated, intact mitochondria is stimulated strongly by carnitine. Why?

What are the first two steps of β oxidation of fatty acids after transport into the mitochondria? Show structures and indicate where any cofactors participate. Draw the four basic steps in the oxidation of a saturated fatty acid (the β-oxidation pathway). Show structures, name enzymes, and indicate where any cofactors participate. Show the last step in the sequence of the four reactions in the β-oxidation pathway for fatty acid degradation. Include the structures of reactant and product, the enzyme name, and indicate where any cofactors participate. One of the steps in fatty acid oxidation in mitochondria involves the addition of water across a double bond. What is the next step in the process? Show structures and indicate where any cofactor(s) participate(s).

In the citric acid cycle, a double bond is introduced into a four-carbon compound containing the —CH2—CH2— group, producing fumarate. Show a similar reaction that occurs in the β-oxidation pathway.

Write a balanced equation for the β oxidation of palmitoyl-CoA, a 16-carbon, fully saturated fatty acid, and indicate how much of each product is formed.

The total degradation of a fatty acid with an odd number of carbons yields acetyl-CoA and another compound, X. Show the structure of X, and describe into what intermediate of citric acid cycle it is converted.

Draw the structure of one ketone body, and describe circumstances under which you would expect to find high concentrations of this compound in an organism. What are ketone bodies and why do they form during diet? The reaction sequence that leads to fatty acid synthesis includes (1) condensation, (2) first reduction reaction, (3) dehydration, and (4) second reduction. Show the first reduction reaction, with any required cofactors. The reaction sequence that leads to fatty acid synthesis includes (1) condensation, (2) first reduction reaction, (3) dehydration, and (4) second reduction. Show the second reduction reaction, with any required cofactors.

Amino Acid Metabolism

Which of these is not a protease that acts in the small intestine? A) Chymotrypsin B) Pepsin C) Enteropeptidase D) Secretin E) Trypsin In amino acid catabolism, the first reaction for many amino acids is a(n): A) decarboxylation requiring thiamine pyrophosphate (TPP). B) hydroxylation requiring NADPH and O2. C) oxidative deamination requiring NAD+. D) reduction requiring pyridoxal phosphate (PLP). E) transamination requiring pyridoxal phosphate (PLP). The coenzyme involved in a transaminase reaction is: A) biotin phosphate. B) lipoic acid. C) nicotinamide adenine dinucleotide phosphate (NADP+). D) pyridoxal phosphate (PLP). E) thiamine pyrophosphate (TPP).

Pyridoxal phosphate is a cofactor in this class of reactions: A) acetylation. B) desulfuration. C) methylation. D) reduction. E) transamination.

Glutamate is metabolically converted to α-ketoglutarate and NH4

+ by a process described as: A) deamination. B) hydrolysis. C) oxidative deamination. D) reductive deamination. E) transamination.

The conversion of glutamate to an α-ketoacid and NH4

+: A) does not require any cofactors. B) is a reductive deamination. C) is accompanied by ATP hydrolysis catalyzed by the same enzyme. D) is catalyzed by glutamate dehydrogenase. E) requires ATP.

Urea synthesis in mammals takes place primarily in tissues of the: A) brain. B) kidney. C) liver. D) skeletal muscle. E) small intestine.

Which substance is not involved in the production of urea from NH4

+ via the urea cycle? A) Aspartate B) ATP C) Carbamoyl phosphate D) Malate E) Ornithine

Which of these directly donates a nitrogen atom for the formation of urea during the urea cycle? A) Adenine B) Aspartate C) Creatine D) Glutamate E) Ornithine

Conversion of ornithine to citrulline is a step in the synthesis of: A) aspartate. B) carnitine. C) pyruvate. D) tyrosine. E) urea.

In the urea cycle, ornithine transcarbamoylase catalyzes: A) cleavage of urea to ammonia. B) formation of citrulline from ornithine and another reactant. C) formation of ornithine from citrulline and another reactant. D) formation of urea from arginine. E) transamination of arginine.

Which of the following amino acids are essential for humans? A) alanine B) aspartic acid C) asparagine D) serine E) threonine

If a person's urine contains unusually high concentrations of urea, which one of the following diets has he or she probably been eating recently? A) High carbohydrate, very low protein B) Very high carbohydrate, no protein, no fat C) Very, very high fat, high carbohydrate, no protein D) Very high fat, very low protein E) Very low carbohydrate, very high protein

Which of these amino acids can be directly converted into a citric acid cycle intermediate by transamination? A) glutamic acid B) serine C) threonine D) tyrosine E) proline

Which of these amino acids are both ketogenic and glucogenic?

1. Isoleucine 2. Valine 3. Histidine 4. Arginine 5. Tyrosine

A) 1 and 5 B) 1, 3, and 5 C) 2 and 4 D) 2, 3, and 4 E) 2, 4, and 5

The amino acids serine, alanine, and cysteine can be catabolized to yield: A) fumarate. B) pyruvate. C) succinate. D) α-ketoglutarate. E) none of the above.

Serine or cysteine may enter the citric acid cycle as acetyl-CoA after conversion to: A) oxaloacetate. B) propionate. C) pyruvate. D) succinate. E) succinyl-CoA.

Nonessential amino acids: A) are amino acids other than those required for protein synthesis. B) are not utilized in mammalian proteins. C) are synthesized by plants and bacteria, but not by humans. D) can be synthesized in humans. E) may be substituted with other amino acids in proteins.

An amino acid that does not derive its carbon skeleton, at least in part, from α-ketoglutarate is: A) arginine. B) glutamate. C) glutamine. D) proline. E) threonine.

An amino acid that does not derive its carbon skeleton, at least in part, from oxaloacetate is: A) aspartate. B) lysine. C) methionine. D) proline. E) threonine.

Short Answer Questions

Draw the structures of reactants and products in the transamination in which glutamate and pyruvate are the starting materials. What cofactor is required for this reaction?

Give the name and draw the structure of the α-keto acid resulting from the following amino

acids that undergo transamination with α-ketoglutarate: (a) aspartate; (b) alanine. Show the reaction in which ammonia is formed from glutamate; include any required cofactors. Describe the reactions and the role of the glucose-alanine cycle. Describe the three general mechanisms for disposing of excess nitrogen obtained in the diet.

Which organisms use each mechanism? During starvation, more urea production occurs. Explain this observation (in 20 words or less). Name at least three amino acids that can be converted directly (in one step) into pyruvate or

any citric acid cycle intermediate, and name that intermediate formed from each. Degradation of amino acids yields compounds that are common intermediates in the major metabolic pathways. Explain the distinction between glucogenic and ketogenic amino acids in terms of their metabolic fates.