BCH ex4 – Flashcards

1. What is the final electron acceptor of the cytochrome b6f complex? A) ferredoxin B) NADP+ C) P700 D) plastocyanin

2. What are the benefits of cyclic electron flow in photosynthesis? A) Energy recovered in NADPH B) Energy conserved in proton gradient C) Promotes ATP synthesis by chemiosmosis D) Both B and C E) All of the above

3. The amino acid ______ acts as a transfer system for NH3, safely allowing the toxic molecule to be transported from the liver to the kidneys. A) alanine B) tyrosine C) glutamine D) aspartate E) proline

4. Reaction 3 in the first round of fatty acid synthesis involves the transfer of an acetyl group A) from acetyl-Cys to malonyl-ACP B) from malonyl-ACP to acetyl-Cys C) from acetyl-CoA to malonyl-ACP D) from acetyl-CoA to malonyl-CoA E) from malonyl-CoA to acetyl-ACP

5. Cholesterol and other lipids are transported from tissues to the liver by ______. A) LDL B) malonyl-CoA C) citrulline D) HDL E) chylomicrons

6. Which of the following is an accurate representation of a transaminase reaction? A) Ala → pyruvate B) Cys → pyruvate C) Ser → pyruvate D) Asp → oxaloacetate E) Both A and D

7. What hormone that is produced in adipose tissue signals satiety? A) adiponectin B) cholecystokinin C) leptin D) ghrelin E) amylin

8. Which of the following is an accurate example of the synthesis of a nonessential amino acid? A) Asp → pyruvate B) Ala → pyruvate C) Ser → Ala D) Glu → Pro

9. Isoprene units form the carbon skeleton of ______. A) HDL B) propionyl-CoA C) malonyl-CoA D) cholesterol E) ketone bodies

10. The cofactor ______ is used to transfer C1 units such as methyl, formyl, and methenyl groups. A) biotin B) TPP C) lipoamide D) FAD E) THF

11. Lipoproteins formed in the intestinal mucosal cells are ______. A) HDL B) IDL C) LDL D) chylomicrons E) triglycerides

12. During the oxidation of water, where do the protons go? A) thylakoid lumen B) stroma C) space between inner and outer chloroplast membrane D) cytosol E) protons are not released but transferred to proteins for metabolic use

13. Which enzyme has a higher affinity for glucose at physiological concentrations? A) hexokinase B) glucokinase

14. The enzyme ______ is critical to regulating nitrogen metabolism in humans. A) glutamine transferase B) nitrogenase C) glutamine synthetase D) lysozyme E) proteasome

15. In a variation of the Cori cycle, what amino acid is transported from the muscle to the liver? A) glycine B) glutamate C) aspartate D) alanine E) glutamine

16. The photosynthetic pathway that results in the formation of NADPH is called A) CF1CFo B) Tyrosyl radical C) OEC D) Antennae complex E) Z scheme

17. Digestion of triacylglycerols is aided by the cholesterol derivatives collectively known as ______. A) bile acids (bile salts) B) catecholamines C) prostaglandins

18. Glucose is removed from the blood and phosphorylated by the ______ enzyme glucokinase. A) α-adrenergic B) Cori cycle C) kidney D) leptin E) liver

19. Indicate whether heme groups occur in chloroplasts, mitochondria, or both. A) chloroplasts B) mitochondria C) both

20. Deoxyribonucleotides are synthesized by ______ of a ribonucleotide's 2ʹ′ carbon. A) oxidation B) decarboxylation C) reduction D) dehydration E) hydration

21. The breakdown product of valine is succinyl-CoA. This amino acid would be classified as A) ketogenic B) glucogenic C) Both glucogenic and ketogenic

22. In fatty acid catabolism, chain shortening occurs at the _____ end of the fatty acyl chain. A) methyl B) thioester C) both the metyl and thioester

23. How many photons will be involved in the transfer of 4 electrons from PSII to 2 NADP+? A) 4 B) 2 C) 8 D) 6

24. ______ is the precursor of aromatic amino acid biosynthesis in plants and bacteria. A) Tryptophan B) Chorismate C) Arginine D) Pyruvate E) Glutamine

25. Which of the following aspects of brown adipose tissue is responsible for its ability to generate heat? A) brown adipose tissue contains many small fat droplets instead of one large globule B) blood flow to brown adipose tissue is larger than to white adipose tissue C) brown adipose tissue has receptors for norepinephrine D) the uncoupling protein allows fatty acid oxidation without ATP production E) none of the above

26. Fatty acid oxidation occurs in A) mitochondria and peroxisomes B) mitochondria and chloroplasts C) mitochondria, chloroplasts, and peroxisomes D) none of the above

27. If carbon dioxide is used as a substrate, the major products of rubisco are _____; if oxygen is used as a substrate, the major products of rubisco are _____. A) 2 molecules of 3-phosphoglycerate; 2-phosphoglycolate and 3-phosphoglycerate B) 2 molecules of 3-phosphoglycerate; glyoxylate and 3-phosphoglycerate C) 3-phosphoglycerate and glyceraldehyde-3-phosphate; 2-phosphoglycolate and 3-phosphoglycerate D) 3-phosphoglycerate and glyceraldehyde-3-phosphate; glyoxylate and 3-phosphoglycerate E) none of the above

28. The neurotransmitters DOPA, dopamine, epinephrine, and norepinephrine are synthesized from the amino acid ______. A) tryptophan B) tyrosine C) phenylalanine D) glutamine E) aspartate

29. What hormone that is commonly produced in typical body fat has very little production in visceral fat (also known as abdominal fat)? A) leptin B) resistin C) neuropeptide Y D) ghrelin E) cholecystokinin

30. Which intermediate is involved in both fatty acid and cholesterol synthesis? A) α-ketoglutarate B) acetoacetate C) acetoacetyl thioester D) isoprene E) acetone

31. Which of the following metabolic pathways occurs exclusively in the cytosol? A) citric acid cycle B) ketogenesis C) urea cycle D) amino acid degradation E) fatty acid synthesis

32. The E°ʹ′ for the half-reaction: N2 + 6 H+ + 6 e- ⇔ 2 NH3 is -0.34 V. The reduction potential of the nitrogenase component that donates electrons for nitrogen reduction is about -0.29V. ATP hydrolysis apparently induces a conformational change in the protein that alters its reduction potential (by about 0.11 V). Does this change increase or decrease the E°ʹ′ of the electron donor? A) increase B) decrease

33. A deficiency of carnitine results in muscle cramps, which are exacerbated by fasting or exercise. What is the biochemical explanation for this muscle cramping? A) Carnitine is used to directly contribute acetyl-CoA to the TCA cycle, to thereby generate energy. B) Carnitine is the acyl carrier that allows β-oxidation of fatty acids to occur in the mitochondrial matrix, to thereby generate energy. C) Carnitine is the cofactor used by acyl-CoA dehydrogenase in the first step of β-oxidation. D) Carnitine directly donates electrons to the electron transport chain, which generates the proton gradient utilized in ATP synthesis.

34. How is ATP synthesis during photosynthesis different from ATP synthesis during mitochondrial oxidative phosphorylation? A) Mitochondrial ATP synthesis produces more ATP per turn of ATP synthase. B) The pH gradient during photophosphorylation is higher. C) The electrical component of the proton gradient in photosynthesis is higher than that in mitochondria. D) There is no difference between the two.

35. What is the FIRST event to occur in the light reactions of photosynthesis? A) Oxidation of P680 chlorophyll B) Absorption of a photon of light energy by PSII reaction center C) Absorption of a photon of light energy by PSI reaction center D) Oxidation of H2O by the OEC (oxygen evolving center) E) Reduction of plastoquinone

36. Protein kinase A is responsible for A) activating glycogen synthase B) inactivating glycogen synthase C) activating phosphoylase kinase D) A and C E) B and C

37. Glycogen phosphorylase is allosterically ______ by ATP. A) activated B) inhibited C) unaffected

38. Which of the following is NOT a phase of the Calvin cycle? A) carbon fixation B) reduction C) photoxidation D) regeneration

39. Which of the following statements about the Oxygen Evolving Center (OEC) is false? A) It is located at the lumenal surface. B) It is identical to the OEC in mitochondria. C) It contains a manganese catalyst. D) It utilizes a tyrosyl radical in the reaction mechanism. E) None of the above statements are false.

40. Which of the following does NOT participate in the regulation of fatty acid synthesis? A) Feedback inhibition by palmitoyl-CoA B) Activation by citrate C) Activation by malonyl-CoA D) acetyl-CoA carboxylase E) All of the above regulate fatty acid synthesis

41. What carbon compound is the net product of fixing CO2 in the Calvin cycle? A) glucose B) ribulose-5-phosphate C) oxaloacetate D) glyceraldehyde-3-phosphate E) pyruvate

42. Phosphatidylcholine synthesis begins with activation of phosphocholine by the transfer of ______, which is then displaced by ______. A) AMP, phosphatidate B) CMP, diacylglycerol C) UMP, diacylglycerol D) CMP, phosphatidate E) AMP, diacylglycerol

43. The electrons used to convert an NDP to a dNDP ultimately come from A) NADPH B) fumarate C) uric acid D) iron E) IMP

44. Which of the following represents the correct order of the transaminase mechanism? i. amine group transferred from PLP to keto acid substrate ii. amine group transferred to PLP and keto acid product released iii. keto acid substrate binds iv. amine donor binds v. amino acid product released A) iv, ii, iii, i, v B) ii, iii, iv, v, i C) iii, ii, iv, i, v D) i, ii, iii, iv, v E) iv, i, iii, ii v

45. Diabetes mellitus Type ____ is an autoimmune response that destroys pancreatic cells and Type ____ occurs due to insulin resistance. In Type II, the liver responds by synthesizing ____ glucose. A) II, I, more B) II, I, less C) II, I, the same amount of D) I, II, more E) I, II, less

46. What molecule is necessary to transport fatty acyl-CoA into mitochondria? A) citrate B) malate C) aspartate D) oxaloacetate E) carnitine

47. The end products of pyrimidine catabolism are: A) β-alanine, uric acid B) uric acid and allantoin C) β-alanine, β-aminoisobutyrate D) succinic acid, fumarate E) none of the above

48. Which of the following best describes the order for the conversion of glycerol-3-phosphate into a triacylglycerol? A) 1 phosphatase reaction then 3 acyltransferase reactions B) 1 acyltransferase reaction, 1 phosphatase reaction, then 2 more acyltransferase reactions C) 2 acyltransferase reactions, 1 phosphatase reaction, then 1 acyltransferase reaction D) 3 acyltransferase reactions then 1 phosphatase reaction E) 1 acyltransferase reaction, 1 phosphatase reaction, 1 acyltransferase reaction, 1 phosphatase reaction,then 1 acyltransferase reaction

49. Which of the following would most likely be involved in limiting the signaling effect of insulin? A) G protein dephosphorylase B) tyrosine phosphatase C) tyrosine kinase D) cAMP phosphodiesterase E) G protein kinase

50. Identify the amine acceptor in the following transamination reaction. Glu + amine acceptor --> Asp + α-ketoglutarate A) oxaloacetate B) pyruvate C) glutamine D) α-ketoglutarate E) acetoacetic acid

51. Which of the following best explains the chain of events that occurs when glucagon binds to its receptor? A) activation of protein kinase A, activation of G protein, activation of adenylate cyclase, production of cAMP B) activation of adenylate cyclase, production of cAMP, activation of protein kinase A, activation of G protein C) production of cAMP, activation of adenylate cyclase, activation of protein kinase A, activation of G protein D) activation of G protein, activation of protein kinase A, activation of adenylate cyclase, production of cAMP E) activation of G protein, activation of adenylate cyclase, production of cAMP, activation of protein kinase A

52. How does the glutamate dehydrogenase reaction contribute to amino acid biosynthesis and also function as an anaplerotic reaction for the TCA cycle? A) It produces glutamate through the condensation of α-ketoglutarate and ammonia. B) It produces glutamate through the transamination of aspartate to form asparagine. C) Glutamate can be deaminated to form the TCA intermediate α-ketoglutarate. D) A and C E) B and C

53. Does the quantum yield of photosynthesis increase or decrease (or neither) for systems where the proportion of cyclic electron flow through Photosystem I increases? A) The quantum yield decreases. B) The quantum yield increases. C) There is no change in the quantum yield.

54. Decreased carnitine acyltransferase activity along with reduced activity of the mitochondrial electron transport chain have been observed in obese individuals. Which of the following processes are being affected? A) Transport of fatty acids from the cytosol to the mitochondria B) Oxidation of NADH C) Synthesis of malonyl-CoA D) A and B E) A, B and C

55. How many ATP-equivalent molecules will be generated by β oxidation of a saturated fatty acid with 19 carbons? (1 QH2 = 1.5 ATP; 1 NAD(P)H = 2.5 ATP) A) 122.5 ATP B) 128.5 ATP C) 126.5 ATP D) 117 ATP E) 130.5 ATP

56. Ribose phosphate pyrophosphokinase catalyzes the conversion of ribose-5-phosphate to PRPP. How do ADP and GDP regulate this enzyme? A) They act as allosteric inhibitors. C) They act as feedback inhibitors. B) The act as allosteric activators. D) They act as feed-forward activators.

57. Both fatty acid oxidation and glucose oxidation by glycolysis lead to the formation of large amounts of ATP. A cell preparation containing all the enzymes required for either pathway cannot generate ATP when a fatty acid or glucose is added, unless a small amount of _______ is also added to the preparation. A) pyruvate B) carnitine C) ATP D) citrate

1. Following prolonged starvation, ______ are used as fuel by the brain. A) leptins B) cholesterol C) fatty acids D) ketone bodies E) sucrose

2. After photon absorption, the reduction potential of P680 chlorophyll is A) decreased B) increased C) unchanged

3. The nonessential amino acids _____ and _____ are synthesized from essential amino acids. A) cysteine B) tyrosine C) methionine D) A and B E) B and C

4. Which enzyme is the better sensor of glucose concentration? A) hexokinase B) glucokinase

5. Insulin is released from pancreatic ___ cells in response to ____ blood glucose. A) β; low B) β; high C) α; low D) α; high

6. What is the product of fatty acid activation? A) acyladenylate B) pyrophosphate C) acyl-CoA D) acyl ester E) acyl-carnitine

7. During fuel abundance, excess ____ is (are) catabolized to acetyl-CoA , which is used in fatty acid synthesis. A) glucose B) amino acids C) nucleotides D) A and B E) A, B and C

8. When a growing fatty acid is not attached to the ACP, it is attached to a _____ residue of the fatty acid synthase complex. A) Cys B) Ser C) Tyr D) Glu E) His

9. Which of the pathways for nucleotide biosynthesis builds the base first and then attaches it to a PRPP molecule? A) purine B) pyrimidine C) both purine and pyrimidine

10. The site of ATP synthesis in the chloroplast is the _____ membrane. A) stroma B) inner mitochondrial C) plasma D) thylakoid E) outer mitochondrial

11. Fatty acid activation occurs in the _____. A) mitochondrion B) cytosol C) nucleus D) peroxisome

12. What transport system moves activated fatty acids from the cytosol to the mitochondrial matrix? A) triacylglycerol shuttle B) glycerol phosphate shuttle C) acyl adenylate shuttle D) lipoprotein shuttle E) carnitine shuttle

13. Which of the following does NOT describe a way in which an absorbed photon can dissipate its excitation energy? A) Heat conversion B) Photooxidation C) Fluorescence D) Photoreduction E) Exciton transfer

14. The active group of photosystem I is known as _____. A) P800 B) P700 C) P660 D) P650 E) P450

15. Nitrogen is supplied to the urea cycle by A) glutamate B) glutamine C) aspartate D) A and C E) B and C

16. The major sugar transported to nonphotosynthesizing plant cells is: A) sucrose B) fructose C) glucose D) ribose E) none of the above

17. What step controls the activity of both purine and pyrimidine synthesis? A) conversion of IMP to adenylosuccinate for AMP production B) conversion of IMP to xanthosine monophosphate for GMP production C) conversion of ribose-5-phosphate to 5-phosphoribosyl pyrophosphate (PRPP) D) conversion of UTP to CTP E) ribonucleotide reductase

18. What hormone is most likely responsible for the body weight set-point? A) adiponectin B) cholecystokinin C) leptin D) ghrelin E) all of the above

19. All transaminases require the cofactor A) thiamine pyrophosphate B) FAD C) NAD+ D) pyridoxyl-5'-phosphate E) lipoamide

20. Which enzyme is the most important control point for fatty acid synthesis? A) ATP-citrate lyase B) transacylase C) 3-ketoacyl-ACP reductase D) 3-hydroxyacyl-ACP dehydrase E) acetyl-CoA carboxylase

21. In plants and cyanobacteria, Photosystem II ______, and Photosystem I ______. A) oxidizes H2O, reduces NAD+ B) oxidizes H2O, reduces NADP+ C) oxidizes O2, reduces FAD D) oxidizes H2O, reduces FAD E) none of the above are true

22. Which of the following citric acid cycle intermediates can be converted to aspartate via transamination? A) succinate B) fumarate C) α-ketoglutarate D) citrate E) oxaloacetate

23. Which of the following shows the correct movement of electrons in the Z-scheme of photosynthesis? A) H2O → P700 → plastoquinone → cytochrome b6f → plastocyanin → P680 → ferredoxin → NADP+ B) H2O → P680 → plastocyanin → cytochrome b6f → plastoquinone → P700 → ferredoxin → NADP+ C) H2O → P680 → plastoquinone → ferredoxin → plastocyanin → P700 → cytochrome b6f → NADP+ D) H2O → P680 → plastoquinone → cytochrome b6f → plastocyanin → P700 → ferredoxin → NADP+ E) H2O → P680 → ferredoxin → plastoquinone → P700 → cytochrome b6f → plastocyanin → NADP+

24. Nonketotic hyperglycinemia (NKH) is an inborn error of metabolism characterized by high levels of glycine in the blood, urine, and cerebrospinal fluid. What enzyme is most likely nonfunctional in patients with NKH? A) serine transaminase B) glycine transaminase C) serine deaminase D) glycine cleavage system

25. What is the net effect of the glucose-alanine cycle? A) The transfer of free energy from muscles to the liver B) The transfer of free energy from the liver to muscles C) The transfer of nitrogen from the liver to muscles D) The transfer of nitrogen from muscles to the liver

26. What molecule is able to move across the mitochondrial membrane and is thus used to "transfer" acetyl-CoA from the mitochondria to the cytosol? A) acetate B) oxaloacetate C) α-ketoglutarate D) citrate E) succinate

27. In the process of nitrification, nitrate reductase converts _____ into _____. A) nitrate; nitrogen B) nitrate; ammonia C) nitrate; nitrite D) nitrate; nitric oxide E) nitrogen; nitrate

28. What enzyme associated with the urea cycle enzyme is activated by N-acetylglutamate? A) carbamoyl phosphate synthetase B) glutamate dehydrogenase C) argininosuccinate synthetase D) arginase E) ornithine transcarbamoylase

29. What are the energy requirements for the synthesis of one molecule of palmitate (C16) from eight molecules of acetyl-CoA? A) 16 NADPH, 15 ATP B) 16 NADPH, 8 ATP C) 16 NADPH, 7 ATP D) 14 NADPH, 15 ATP E) 14 NADPH, 7 ATP

30. Glycogen phosphorylase is allosterically ______ by AMP. A) activated B) inhibited C) unaffected

31. A 15-C saturated fatty acid will undergo how many rounds of regular β-oxidation? A) 5 B) 6 C) 7 D) 8 E) Odd-chain fatty acids do not undergo β-oxidation.

32. The Z-scheme of photosynthesis produces a 3:2 ratio of ATP:NADPH. How does a plant compensate when starch or sucrose is being synthesized? A) no changes need to be made since there is more ATP available from the light reactions than actually needed for carbon fixation B) no cyclic photophosphorylation can occur C) more cyclic photophosphorylation must occur D) more NADPH must be made E) none of the above

33. Phosphatidylcholine synthesis begins with activation of phosphocholine by the transfer of ______, which is then displaced by ______. A) AMP, phosphatidate B) CMP, diacylglycerol C) UMP, diacylglycerol D) CMP, phosphatidate E) AMP, diacylglycerol

34. A deficiency of carnitine results in muscle cramps, which are exacerbated by fasting or exercise. What is the biochemical explanation for this muscle cramping? A) Carnitine is used to directly contribute acetyl-CoA to the TCA cycle, to thereby generate energy. B) Carnitine is the acyl carrier that allows β-oxidation of fatty acids to occur in the mitochondrial matrix, to thereby generate energy. C) Carnitine is the cofactor used by acyl-CoA dehydrogenase in the first step of β-oxidation. D) Carnitine directly donates electrons to the electron transport chain, which generates the proton gradient utilized in ATP synthesis.

35. What amino acid is the precursor for the neurotransmitters epinephrine and norepinephrine? A) tryptophan B) serine C) tyrosine D) aspartate E) glutamate

36. Which of the following is NOT an aspect of Photosystem II? A) Electrons from PSII are passed to plastoquinone. B) PSII oxidizes 2 H2O to produce 1 O2 involving 2 photooxidations. C) The reaction center chlorophyll absorbs a wavelength of 680 nm. D) A manganese catalyst extracts electrons from water. E) All of the above are true.

37. What are the two small metabolites at the "crossroads" of metabolism? A) pyruvate and citrate B) oxaloacetate and glyceraldehyde-3-phosphate C) pyruvate and acetyl-CoA D) α-ketoglutarate and malonyl-CoA E) glyceraldehyde-3-phosphate and dihydroxyacetone phosphate

38. Which of the following does NOT participate in the regulation of fatty acid synthesis? A) Feedback inhibition by palmitoyl-CoA B) Activation by citrate C) Activation by malonyl-CoA D) acetyl-CoA carboxylase E) All of the above regulate fatty acid synthesis

39. Red blood cells lack mitochondria. What metabolic pathway(s) would be involved in ATP production in the red blood cell? A) glycolysis B) TCA cycle C) glycolysis and TCA cycle D) fatty acid oxidation E) catabolism of ketone bodies

40. Which of the following amino acids is properly paired with the amino acid from which it is derived? A) Gln: Asp B) Pro: Ala C) Arg: Lys D) Tyr: Phe E) Ser: Cys

41. The breakdown products of isoleucine are succinyl-CoA and acetyl-CoA. This amino acid would be classified as A) ketogenic B) glucogenic C) Both glucogenic and ketogenic

42. Which of the ketone bodies can be decarboxylated non-enzymatically? A) cholesterol B) acetoacetate C) 3-hydroxybutyrate D) acetone

43. Insulin binding initiates a cascade that eventuates in the activation of ____ . A) protein phosphatase I B) glycogen phosphorylase C) glycogen synthase D) A and B E) A and C

44. What is the FIRST event to occur in the light reactions of photosynthesis? A) Oxidation of P680 chlorophyll B) Absorption of a photon of light energy by PSII reaction center C) Absorption of a photon of light energy by PSI reaction center D) Oxidation of H2O by the OEC (oxygen evolving center) E) Reduction of plastoquinone

45. If a reaction that included all of the enzymes involved in fatty acid synthesis was supplied with excess ATP, NADPH, acetyl-CoA and 14CO2 (where the carbon was a 14C-label), where would the labeled carbon appear in the finished fatty acid? A) odd-numbered carbons B) even-numbered carbons C) every third carbon D) every fifth carbon E) no carbons would be labeled

46. Complete the following reaction (P680* represents an excited state; P680- or P680+ represents the gain or loss of an electron): P680 + light → _____ → _____ A) P680*; P680- + H+ B) P680*; P680+ + e- C) P680-; P680* D) P680+; P680* E) none of the above

47. Diabetes mellitus Type ____ is an autoimmune response that destroys pancreatic cells and Type ____ occurs due to insulin resistance. In Type II, the liver responds by synthesizing ____ glucose. A) II, I, more B) II, I, less C) II, I, the same amount of D) I, II, more E) I, II, less

48. Ketogenic amino acids are enzymatically broken down to acetoacetate or ______. A) citrulline B) acetone C) pyruvate D) hydroxybutarate E) acetyl-CoA

49. Which of the following describes photorespiration? A) consumes ATP B) consumes NADPH C) produces CO2 D) consumes oxygen E) all of the above

50. Which of the following is NOT associated with metabolic syndrome? A) obesity B) insulin resistance C) hypertension D) high proportion of visceral fat E) Type I diabetes

51. Atoms from the amino acids ______ are utilized in purine biosynthesis. A) Asp, Gly, Gln B) Asp, Gly, Gln, Phe C) Asp, Gln, Phe D) Asn, Gly, Gln, Phe E) none of the above

52. How many ATP-equivalent molecules will be generated by β oxidation of a saturated fatty acid with 18 carbons? (1 QH2 = 1.5 ATP; 1 NAD(P)H = 2.5 ATP) A) 122 ATP B) 112 ATP C) 120 ATP D) 110 ATP E) none of the above

53. An infant seemed normal at birth but was diagnosed at the age of 3 months with a pyruvate carboxylase deficiency. She suffered from lactic acidosis and ketosis, and had poor muscle tone and seizures. Which of the following would contribute to her symptoms? A) Accumulation of pyruvate and alanine B) Accumulation of acetyl-CoA C) Lack of oxaloacetate D) A and B E) A, B and C

54. The first three reactions (#1, #2, #3) of the β oxidation pathway are similar to three reactions of the citric acid cycle. Which reactions are these? A) oxaloacetate citrate isocitrate α-ketoglutarate B) citrate isocitrate α-ketoglutarate succinyl-CoA C) succinate fumarate malate oxaloacetate D) α-ketoglutarate succinyl-CoA succinate fumarate

55. The herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) blocks electron flow from Photosystem II to Photosystem I. What is the effect on oxygen production and photophosphorylation when DCMU is added to plants? A) The production of oxygen continues, but ATP synthesis is blocked. B) The production of oxygen is blocked, but ATP synthesis continues. C) The production of oxygen is blocked and ATP synthesis stops. D) There is no effect on either process.

56. Amidophosphoribosyltransferase catalyzes the committed step of the IMP synthetic pathway and uses PRPP as its substrate. How would this enzyme be affected by PRPP? A) It acts as an allosteric inhibitor. C) It acts as a feedback inhibitor. B) It acts as an allosteric activator. D) It acts as a feed-forward activator.

57. Threonine deaminase catalyzes the committed step of the biosynthetic pathway leading to the branched-chain amino acid isoleucine. The enzyme catalyzes the dehydration and deamination of threonine to α-ketobutyrate (below), which is later converted to isoleucine. Threonine deaminase is a tetramer that has a low affinity T form and a high affinity R form and is allosterically regulated. The activity of this enzyme was measured at increasing concentrations of the substrate threonine in the absence (curve A) and presence (curve B) of isoleucine. Based on these data, what is the effect of isoleucine on threonine deaminase activity and to which form of the enzyme does isoleucine bind? A) Isoleucine is an allosteric activator and binds to the T form. B) Isoleucine is an allosteric inhibitor and binds to the R form. C) Isoleucine is an allosteric activator and binds to the R form. D) Isoleucine is an allosteric inhibitor and binds to the T form. E) Isoleucine is a competitive inhibitor and binds to the T form.