Problem Set 2 (multiple choice) Biochemistry 3300

Transcription

1 1. What classes of reactions do Lyases catalyse? a) Bond formation coupled with ATP hydrolysis b) Isomerizations c) Group elimination to form double bonds d) Transfer of functional groups e) Hydrolysis reactions 2. Which of the following Metal ions is not likely to be found in the catalytic center of a redox enzyme? a) Fe 2+ b) Co 3+ c) Ca 2+ d) Mn 2+ e) Fe Which of the following is not a catalytic mechanism in enzymatic catalysis a) Acid-Base catalysis b) Covalent catalysis c) Metal ion catalysis d) Electrostatic catalysis e) Preferential binding to the product 4. You are given a list of E.C. numbers by your independent study supervisor, but from looking at it you feel that one of the enzymes does not exist. Which one? a) b) c) d) e) Which of the following statements is not true: a) All living organisms try to be in equilibrium. b) A living cell tries to maintain a steady state. c) Maintaining a steady state is coupled to a flux of metabolites d) Organisms use metabolic processes to obtain the free energy they need to carry out various functions. e) Chemotrophs rely on chemical compounds derived from other organisms. 6. The imidazole side chain of histidine can function as either a general acid catalyst or a general base catalyst because: a) in the physiological ph range both H + and OH are present at high concentrations. b) in the physiological ph range, the nitrogen in the ring can be easily protonated/deprotonated. c) one guanidino group is protonated, and the other is deprotonated at physiological ph. d) the imidazole group is a strong reducing agent at physiological ph. e) the sulfur atoms in the ring can either gain or lose a proton at physiological ph.

2 7. Which of the following is not true about enzymes? a) Enzymes catalyze the reaction in only the forward direction. b) Enzymes are often very specific for their substrates. c) Enzyme activities can often be regulated. d) Enzymes typically act under milder conditions of temperature and ph than chemical catalysts. e) Enzymes typically catalyze reactions at much higher rates than chemical catalysts. 8. Which of the following amino acid residues would not provide a side chain for acid-base catalysis? a) leucine b) serine c) lysine d) aspartic acid e) histidine 9. Metabolic pathways are a series of consecutive enzymatic reactions that produce specific products. Reactants, intermediates and products are referred to as: a) Anabolites b) Catabolites c) Metabolites d) Orthobiltes e) Anabolica 10. The reaction below belongs to the following type of biochemical reaction: a) Elimination b) Oxidation and reduction c) Reactions that make and brake carbon bonds d) Group-transfer reactions e) Additions 11. Which of the numbered arrows in the figure to the right points toward a high-energy phosphoanhydride bond? a) 1 b) 2 c) 3 d) 4 e) 5

3 12. Choose the best definition for a near-equilibrium reaction: a) Always operates with a favourable free energy change b) Has a free energy change near zero c) Is usually a control point in a metabolic pathway d) Operates very slowly in vivo e) Non of the above 13. The K eq is at 25 C for the following reaction. What is the G ' for this reaction? D-Glucose-6-phosphate D-Fructose-6-phosphate a) 1,700 kj/mol b) 2,870 kj/mol c) +143 kj/mol d) kj/mol e) none of the above 14. If the G' 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. 15. What is the name for the following reaction intermediate? a) Retro Diels-Alder b) Claisen condensation c) Schiff base d) Shuttle mechanism e) Enolate 16. Isotopic tracers are useful in establishing the order of appearance of metabolic intermediates. Give the name for the classical experiment that we have discussed in class? a) Chase experiments b) Manhatten experiments c) Trace experiments d) Race experiments e) Base experiments 17. The Glycolysis was the first metabolic pathway completely traced. The use of metabolic inhibitors was pivotal for the analysis. Which of the following compounds was used to identify Fructose 1,6-bisphosphate as an important metabolite in glycolysis?

4 a) Pyruvate b) GMPPNP c) AMPPNP d) Iodoacetate e) Malonate 18. The standard free-energy changes for the reactions below are given. Phosphocreatine creatine + P G' = 43.0 kj/mol i ATP ADP + P G' = 30.5 kj/mol i What is the overall G' for the following reaction? Phosphocreatine + ADP creatine + ATP a) 73.5 kj/mol b) 12.5 kj/mol c) kj/mol d) kj/mol e) G' cannot be calculated without K '. eq 19. 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. 20. Each biochemical reaction has a characteristic free energy change G 0. Which of the following statements about G 0 is not true for a specific reaction? a) it s a constant b) it depends on K eq c) it is the transformed characteristic free energy change for biological systems d) It is the criterion for the spontaneity of a reaction. e) A and C 21. During glycolysis, the steps between glucose and formation of the triose phosphates. a) consume two ATP and two NADH molecules. b) consume two ATP molecules. c) produce two ADP and two NAD + molecules. d) produce two ATP and two NADH molecules. e) consume two NADH molecules. 22. Given that the standard reduction potential of oxaloacetate is V and the standard reduction potential of NAD + is V. What is the E ' for the oxidation of malate by NAD + : Malate + NAD + Oxaloacetate + NADH + H +

5 a) 4.81 V b) V c) V d) V e) V 23. Sort the following compounds in increasing order by their G 0 of hydrolysis (Starting with the most negative): 1) Phosphoenolpyruvate, 2) ATP, 3) 1,3-Bisphosphoglycerate, 4) Glucose-6 Phosphate a) 3,4,2,1 b) 3,1,2,4 c) 2,1,4,3 d) 1,3,2,4 e) 4,2,3,1 24. The hydrolysis of ATP has a large negative G' ; 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. 25. Which one of the following compounds does not have a large negative free energy of hydrolysis? a) 1,3-bisphosphoglycerate b) 3-phosphoglycerate c) ADP d) Phosphoenolpyruvate e) Thioesters (e.g. acetyl-coa) 26. Nicotinamide Adenine Dinucleotide (NAD) is an electron acceptor in Metabolic Pathways. The resulting change in the absorbance spectrum of NAD+ upon reduction gave rise to a series of coupled assays that are summarized under the following expression: a) Optical Test b) Clinical Test c) Chemical Test d) Tee Test e) Chi Test 27. Complete the following statement correctly: FAD is a prosthetic group,.. a) it is readily exchanged with the solvent. b) it is loosely associated with the protein. c) it is an artificial substitute for NADH. d)... it is tightly bound to the enzyme.

6 e) it needs to be cleaved to activate the enzyme. 28. How many Enzymes are involved in Glycolysis (up to the formation of Pyruvate)? a) 8 b) 5 c) 7 d) 9 e) The two lobes of hexokinase swing together when the substrates bind. Why is this crucial to the catalytic mechanism? a) it will produce enough force to phosphorylate glucose b) it will exclude the inhibitory Mg 2+ ion c) it will exclude water from the catalytic site d) it helps with the product release e) it prevents binding of a different sugar 30. The coenzyme is the oxidizing agent in glycolysis. a) NADH b) NADPH c) NAD + d) NADP + e) FAD 31. Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl-coa? a) FAD b) Lipoic acid c) CoA-SH d) ATP 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 In eukaryotes, the enzymes that catalyze the reactions of citric acid cycle are located in. a) the cell nucleus. b) the endoplasmic reticulum. c) the mitochondria. d) the lysosomes. e) the cytosol.

7 34. The conversion of Galactose to Glucose during galactose metabolism involves changing the configuration at a single carbon of the sugar. What is the name of the enzyme that catalyses this reaction? a) galactose-1-phosphate uridylyl transferase b) UDP-galactose-4-epimerase c) Phosphoglucomutase d) Galactokinase e) Fructose-1-phosphate aldolase 35. Fructose has two potential entry points into glycolysis. What are the names of the two enzymes that are responsible for which entry point a given fructose molecule will use. a) Glycerol phosphate dehydrgenase & triose phosphate isomerase b) Alcohol dehydrogenase & pyruvate decarboxylase c) Fructose-1-phosphate alsolase & aldolase d) Hexokinase & sucrase e) Hexokinase & fructokinase 36. A metabolic pathway that is active catabolically as well as anabolically is called? a) bipolar b) amphother c) bipartite d) departed e) amphibolic 37. Although the pyruvate dehydrgenase complex is huge (app. 4,600,000 Da) it only contains a small number of enzymatic activities. How many can be found in the complex? a) 1 b) 3 c) 5 d) 7 e) 9 Note: I would also have accepted 5 activities 1) decarboxylation to hydroxyethyl TPP 2) acetyl transfer to lipoyllysine 3) acetyl transfer to CoA 4) regeneration of lipoyllysine 5) reduction of NAD Another name for the citric acid cycle is the. a) Cancer Cycle b) Lipmann Cycle c) Karman-Rithoff-Emden-Boyer-Semmelrogge Cycle d) Krebs Cycle e) Tetracorboxylic cycle 39. The Thiazolium ring of thiamine pyrophosphate (TPP) can function as an electron sink similar to a schiff-base. What is the name of the active form TPP after abstraction of the acidic proton? a) Ylid

8 b) Hydride c) Polaron d) Vivid e) Acetylide 40. Who of the following was awarded the Nobel Prize in Physiology or Medicine (1937) for his discoveries in connection with the biological combustion processes, with special reference to vitamin C and the catalysis of fumaric acid"? a) Alexander Fleming, Ernst Boris Chain, Howard W. Florey b) Albert von Szent-Györgyi Nagyrapolt c) Otto Heinrich Warburg d) Carl Ferdinand Cori, Gerty Cori, Bernardo Alberto Houssay e) Hermann Joseph Muller Note: Fun but not covered Hint

9 41. If acetyl-coa labeled with 14 C, as shown in the figure to the right, were used as the substrate for the citric acid cycle, which of the following intermediates would be produced during the first round of the cycle? a) b) c) d) e) 42. Malonate is a competitive inhibitor of succinate dehydrogenase. If malonate is added to a mitochondrial preparation that is oxidizing pyruvate as a substrate, which of the following compounds would you expect to decrease in concentration? a) Citrate b) Fumarate c) Isocitrate d) Pyruvate e) Succinate 43. One reason why arsenic is poisonous is that arsenite ion (AsO 3 3- ) reacts with reduced lipoamide to form a stable complex that cannot be reoxidized. Which of the following metabolic conversions cannot occur in the presence of arsenite? a) Pyruvate + CO 2 oxaloacetate. b) Pyruvate acetyl-coa + CO 2. c) α-ketoglutarate succinyl-coa + CO 2. d) Phosphoenolpyruvate + CO 2 oxaloacetate e) b and c

10 44. The conversion of 1 mol of pyruvate to 3 mol of CO 2 via pyruvate dehydrogenase and the citric acid cycle also yields mol of NADH, mol of FADH 2, 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; Which of the following is correct concerning the metabolic reaction shown below? Pyruvate + NAD + + CoA-SH Acetyl-CoA + NADH + H + + CO 2 a) The enzyme that catalyzes this reaction contains a pyridoxal phosphate prosthetic group. b) This reaction is sometimes referred to as an anaplerotic reaction in that it refills the citric acid cycle when intermediates have been removed for biosynthesis. c) The enzyme that catalyzes this metabolic conversion is activated by high concentrations of ATP. d) This reaction is an oxidative decarboxylation. e) This reaction is catalyzed by an enzyme in the cytosol of the cell. 46. The enzyme of the citric acid cycle that contains an FAD prosthetic group is. a) aconitase b) succinate dehydrogenase c) fumarase d) succinyl-coa synthetase e) malate dehydrogenase 47. The citric acid cycle enzyme contains an iron sulfur cluster. a) aconitase b) isocitrate dehydrgenase c) succinyl-coa synthetase d) malate dehydrogenase e) citrate synthase 48. The citric acid cycle intermediate is found at the beginning and at the end of the citric acid cycle. a) Succinate b) Acteyl-CoA c) Succinyl-CoA d) Citrate e) Oxaloacetate 49. Oxaloacetate uniformly labeled with 14 C (i.e., with equal amounts of 14 C in each of its carbon atoms) is condensed with unlabeled acetyl-coa. After a single pass through the citric

11 acid cycle back to oxaloacetate, what fraction of the original radioactivity will be found in the oxaloacetate? a) all b) 1/2 c) 1/3 d) 1/4 e) ¾ 50. Conversion of 1 mol of acetyl-coa to 2 mol of CO 2 and CoA via the citric acid cycle results in the net production of: a) 1 mol of citrate. b) 1 mol of FADH 2. c) 1 mol of NADH. d) 1 mol of oxaloacetate. e) 7 mol of ATP.