Virginia Commonwealth University BIOC 403 Exam 2_ Biochemistry 403 Exam #2. 25 Q&A

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Virginia Commonwealth University BIOC 403 Exam 2 Biochemistry 403 Exam #2 Name___________Key_____________________ October 10, 2016, Dr. Roesser Multiple Choice (2 points each) 1. A 150 amino... acid protein has ___________ potential amino acid sequences. a. 150 b. 20150 c. 15020 d. 150150 e. None of the above 2. Protein absorbance at 280 nm depends on the number of _________________ amino acids in a protein. a. Aromatic b. Basic c. Nonpolar d. Polar e. All of the above 3. Advantages of having a multisubunit protein include: a. Cooperativity b. Smaller proteins c. Efficiency d. A, B and C e. A and C 4. Urea denatures proteins by: a. Increasing H bonds b. Disrupting H bonds c. Disrupting hydrophobic interactions d. Increasing ionic interactions e. Breaking covalent bonds 5. Energy stabilization of 3o structures comes mainly from: a. Hydrophobic interactions b. H bonds c. ionic interactions d. Covalent bonds e. None of the above 6. Chaperones are thought to function by: a. Forming H bonds b. Increasing hydrophobic interactions c. Lowering EA between energy minima d. Increasing energy stabilization e. All of the above 7. Protein domains have: a. Specific functions b. Independent , stable structures c. Predictable functional motifs d. Structures stabilized by weak forces e. All of the above 8. Enzyme interactions with substrate are best described by: a. Lock and key b. Rigid structure interactions c. Induced fit d. Ionic bonding e. All of the above 9. What is the catalytic power of an enzyme if the rate of the catalyzed reaction is 1X105 molecules/sec and the uncatalyzed rate is 1X10-6 molecules/sec? a. 1X1011 b. 1X10-11 c. 1X10-2 d. 1X10-10 e. 8X102 10. All of the following are true for cofactors except: a. They are usually tightly bound to protein b. They are sometimes vitamins c. Many are cations d. They are non-protein components e. None, all are true 11. For a Lineweaver-Burke plot: a. X intercept= -1/Km b. X intercept= Km/vmax c. X intercept=-vmax d. Y intercept=-vmax e. None of the above 12. Conditions required for Michaelis-Menten kinetics include: a. ES conversion to products is irreversible b. Constant T and pH c. 1 substrate reaction d. [E]<<[S] e. All of the above 13. The enzyme with the highest catalytic efficiency has: a. kcat=2X10-2, Km=3X10-2 b. kcat=3X10-1, Km=5X102 c. kcat=4X104, Km=2X10-4 d. kcat=4X104, Km=1X10-8 e. cannot determine 14. The catalytically active complex of ___________ and _________ is called the _______________. a. apoenzyme; holoenzyme; cofactor b. cofactor; holoenzyme; apoenzyme c. holoenzyme; cofactor; apoenzyme d. apoenzyme; cofactor; holoenzyme e. none are true 15. Proteins generally fold in the following order: a. Hydrophobic collapse, 2o structure interactions, 2o structure formation b. 2o structure formation, 2o structure interaction, ionic collapse c. 2o structure formation, 2o structure interaction, hydrophobic collapse d. 2o structure interaction, ionic collapse, 3o structure interactions e. None of the above 16. Which of the statements about reversible inhibitors are true? a. An uncompetitive inhibitor changes Km but not kcat b. A competitive inhibitor doesn’t change Vmax c. Noncompetitive inhibitors bind to active site d. Uncompetitive inhibitors increase Vmax e. None of the above. 17. Which type of graphical analysis allows exact determination of Km and Vmax? a. Lineweaver-Burke plot b. Direct Vo vs [S] plot c. Haynes-Woolf Plot d. A, B and C e. A and C 18. Competitive inhibitors resemble: a. Substrate b. Product c. Active site d. Enzyme e. None of the above 19. Which amino acid would be most likely to be on the surface of a globular protein? a. Leu b. Val c. Asp d. Trp e. Ile 20. ______________ chromatography separates proteins based on their charge. a. Size exclusion b. Affinity c. Ion exchange d. Solubility e. All of the above 21. Deriving evolutionary relationships by comparing amino acid sequences of the same protein from different organisms is: a. Phylogeny b. Phybotany c. Phlybotemy d. Phyling e. None of the above 22. Polypeptides in a multisubunit protein may be held together by: a. Weak forces b. H bonds c. Ionic interactions d. Cys-Cys disulfide bonds e. All of the above 23. (8 points) Why was ribonuclease A a good choice for Anfinsen’s experiment? Its 3o structure held together by 4 Cys-Cys disulfide bonds 24. (22 points) a. (10 points) Draw a double reciprocal plot representing competitive inhibition. b. (6 points) How does the inhibitor affect the Vmax and Km of the enzyme? c. (2 points) Where on the enzyme does the inhibitor bind? d. (4 points) To what forms of the enzyme does I bind? a. See text b. B. increases Km, doesn’t change Vmax c. Active site d. Binds to Efree, not to ES 25. (24 points) Consider the following 4 enzymes: Enzyme A Enzyme B Enzyme C Enzyme D k1 (1/M sec) 2 X 107 1 X 105 2 X 106 1 X106 k-1 (1/sec) 1 X 102 4 X 103 3 X 103 1 X 103 k2 (1/sec) 5 X 103 2 X 104 2 X 102 5 X 104 cat. rxn rate 3 X 103 2 X 104 5 X 102 6 X 104 uncat. rxn rate 3 X 10-7 2 X 10-4 5 X 10-18 6 X 10-3 A. (4 points) Order the 4 enzymes (A-D) from highest to lowest turnover number. D B A C B. (4 points) Order the 4 enzymes from lowest to highest affinity for substrate. B D C A C. (4 points) Order the enzymes from highest to lowest Km. B D C A D. (4 points) Order the 4 enzymes from lowest to highest affinity for substrate. Any answer E. ( 4 points) Order the 4 enzymes from highest to lowest catalytic efficiency. A D C B F. (4 points) Order the 4 enzymes from highest to lowest catalytic power. C A B D 26. (4 points) Circle the best conditions to use for an enzyme reaction: a. [S] is 4 times the enzyme’s Km b. [S] is ¼ the enzyme’s Km [Show More]

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