Exam_1_2004_Summer

Exam_1_2004_Summer - 497' BCH 4024 INTRODUCTION TO...

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Unformatted text preview: 497' BCH 4024 INTRODUCTION TO BIOCHEMISTRY AND MOLECULAR BIOLOGY DRS. R. D. ALLISON and THOMAS H. MARECI FIRST EXAMINATION: JUNE 3, 2004 Please PRINT your last name neatly on the answer sheet, followed by your initials. Fill in your identification number legibly and accurately. Care has to be exercised in doing this. If you are unsure of how to properly encode your number and name onto the answer sheet, ask a proctor for assistance. If the answer sheet is filled in incorrectly, your sheet will be lost in the computer! Mark the most nearly correct answer on the sheet by completely filling in the appropriate box with the correct type of pencil. If you do not have the correct type of pencil, one can be provided for you. Each question is worth two points. You have two hours to work on the examination. At the end of that time, all answer sheets will be collected. If you need assistance, RAISE YOUR HAND AND WAIT IN YOUR SEAT FOR A PROCTOR. AT NO TIME SHOULD YOU RAISE YOUR EXAMINATION OR YOUR ANSWER SHEET OFF YOUR DESK! Before the start of the examination, remove all notes, books, etc., from your desk. Please have at least one seat between you and any fellow student. DO NOT OPEN THE EXAMINATION UNTIL YOU ARE TOLD TO DO SO BY THE PROCTOR. Take a breath, relax, and do your best. Which of the following bioelements is required in your diet but is still toxic at low concentrations? A) calcium magnesium £9 selenium D) iodine E) sodium Which of the following bonds has the highest bond energy? A) (3—0 B) N-H c c-c Crisco E) 0-H Which of the following is regarded as a colligative property of solutions? A) freezing point elevation an increase in vapor pressure C)‘ boiling point depression B) ‘ the presence of osmotic pressure )/ a decrease in the specific heat capacity. Which of the following is true? A) The pKB of an acid represents the point at which the acid is fully deprotonated. {QM A carboxylic acid is a better buffer at its pKa value than is an amine at its pKa value. ’fC) " At a given pH, the amount of hydroxide ion increases with temperature. An amino acid is a good buffer at its pl value. E) All of the above are false. Your laboratory technician has prepared a solution of 2-tryptophan to be used in a clinical trial. He made up a solution of 1.0 liter of 0.05 M of totally protonated tryptophan. You then tell him to add 4 mL of 10 M KOH. What is the final pH value? (Assume tryptophan has pKd values of 2.43 and 9.44.) A) 1.83 2.33 key" 3.03 D) 8.84 E) 10.04 6. The pKEl value of the side chain of cysteine is about 8.0. The pH of normal blood plasma is 7.4. Using these values, what percentage of cysteine’s side chain is deprotonated? (Choose the closest value. (an 10% (133/ 20% C) 50% D) 80% E) 100% 7. Individual amino acids (not part of a biopolymer) are found in the following ionic structure in the physiological pH range (6.5 to 8.0). A) Only the amino group has a positive charge. B) Only the carboxyl group has a negative charge. C) Only the side chain is charged but the side chain charge depends on the exact pH of the solution and the pKa of the side chain. D) The amino group is negatively charged and the carboxyl group is positively charged (i.e., zwitterion form) but the side chain charge depends on the exact pH of the .N solution and the pKa of the side chain. -"' r E) l The amino group is positively charged and the carboxyl group is negatively charged / (i.e., zwitterion form) but the side chain charge depends on the exact pH of the solution and the pKa of the side chain. 8. Which amino acid can form a disulfide bond? 5% Aspartic acid (Asp) ’T/H) , Cysteine (Cys) Histidine (His) D) Methionine (Met) E) Serine (Set) 9. Which amino acid has the lowest side-chain pKa? Aspartic acid (Asp) LB{ Cysteine (Cys) C) Histidine (His) D) Methionine (Met) E) Serine (Ser) 10. Which of the following pair of amino acids has predominately a positively charged side chain at relatively low pH (<80)? A) Alanine (Ala) and Glycine (Gly) 13) Aspartic acid (Asp) and Glutamic acid (Glu) Lysine (Lys) and Arginine (Arg) f Threonine (Thr) and Tryptophan(Trp) E) Valine (Val) and Isoleucine (He) 11. Which of the following pair of amino acids has a negatively charged side chain at relatively high pH (>80)? A) Alanine (Ala) and Glycine (Gly) " Aspartic acid (Asp) and Glutamic acid (Glu) C) Lysine (Lys) and Arginine (Arg) D) Threonine (Thr) and Tryptophan(Trp) E) Valine (Val) and Isoleucine (lie) 12. The histidine side chain has a pKa value of approximately A) 3.0. B) 4.0. C) 5.0. D); 6.0. 7.0. 13. Which statement is n_ot true concemingarnino acid stereo-isomers? / \ 1 (A) The ()t—CflI‘bOI‘l is a center of chirality for amino acids. B) { All amino acids can occur in one of two stereo—isomeric forms. C) “3 Naturally occurring proteins are constructed of both amino-acid-residue stereo- ” isomers. p)/ Only the L—amino acids are found in naturally occurring proteins. 14. In general, which statement is n_ot true concerning rotations about bonds in a random polypeptide chain? , \- f A) /" Rotation around the bond between the backbone oc-carbon and oc-amino—group is very restricted. B) Rotation around the bond between the backbone oc-carbon and a—carboxyl-group is relatively unrestricted. C) Rotation around the peptide bond is very restricted. D) Rotation around the bond between the backbone ct-carbon and side—chain carbon is relatively unrestricted. 15. Determine the net electrical charge of the following peptide is solution at pH = 9.90. Gly - Glu —Val Amino acid plg information Glycine; 2.3, 9.6 Glutamic acid; 2.2, 4.2, 9.7 Valine; 2.3, 9.6 A) -0.56 By 450 @3le -1.67 D) -191 Hint: Perform all calculation steps to three—significant-figures of accuracy. 16. What is the isoelectic point for the following polypeptide? Arg~His-Gl7—Val Amino acid pKa information Arginine; 2.2, 9.0, 12.5 Histidine; 1.8, 6.0, 9.2 Glycine; 2.3, 9.6 Valine; 2.3, 9.6 A) B) W C) 600” ll) 9% s “f E” +352 {0,73 17. Which statement is n_ot true about protein structure? A) The polypeptide backbone rotate around the peptide bonds is very restricted. B) No two atoms are allowed to approach one another more closely than their van der Waals radii. Within amino acid residues, rotation around bonds to the oc—carbon is not possible. D) Non-covalent bonding stabilizes regular folding of proteins. 18. How many amino acid residues per turn are there in a strand (flat—ribbon) of a B—sheet? {,rg-x.‘ 439/“ 2.0 B) 3.0 C) 3.6 D) 4.4 E) 5.0 19. A B-sheet structure can be formed from the following primary structure elements: A) Segments of polypeptide chain within the same polypeptide. B) Segments of polypeptide chain within different polypeptides. C) Segments of polypeptides running parallel (N to C then N to C). D A Segments of polypeptides running anti-parallel (N to C then C to N). E)‘ /' All of the above. 20. Which secondary structure element is n_ot held together by hydrogen bonding? A) on-helices B) B—sheets C) Type I B-turns p/D} .) Type II B-turns CE? random coil. 21. The protofibrils of keratin (e.g., hair) are composed of the which structural motifs: A) parallel B-sheets. B) anti—parallel B-sheets. PC) a—helices and B-turns. ' coiled coil of two OL—helices. 22. Which statement is most true about the tertiary structure of globular proteins? A) All globular proteins have a defined inside (containing mostly hydrophobic amino acid residues) and outside (containing mostly hydrophilic residues). B) B-sheets can be twisted or wrapped into barrel structures. C) Globular proteins can be made up of a mixture of a—helix and B—sheet secondary 11-x , structural elements. Kb) 3." All ofthe above. L.-/ 23. Which factor dominates the thermodynamics of myoglobin folding? A) The formation of disulfide bonds __B) Internal hydrogen bonds The hydrophobic effect D) Van der Waals interactions E) Charge-charge interactions 24. The tertiary structure of myoglobin and the tertiary structure of individual subunits of hemoglobin consist of the following. A) A single polypeptide chain, folded around a heme group, with 5 ot—helices. B) A single polypeptide chain, folded around a heme group, with 6 OL-helices. C) A single polypeptide chain, folded around a heme group, with 7 ot—helices. C A single polypeptide chain, folded around a heme group, with 8 or—helices. E) A single polypeptide chain, folded around a heme group, with 10 or-helices. 25. Hemoglobin (Hb) has the following quaternary structure characteristics: A) Hb is a tetramer of four identical monomers, where each monomer has the myoglobin structure. B) Hb is a tetramer of four identical monomers, where each type of monomer has a myoglobin—like structure. C) Hb is a tetramer of four different monomers, where each type of monomer has a ,2”é\ myoglobin-like structure. ‘ D) I‘ Hb is a tetramer composed of four monomers two identical-types, where each type \M of monomer has a myoglobin—like structure. 26. Upon O2 binding in hemoglobin, the following occurs: A) The O2 binds to the Fe in heme group. B) The heme group becomes planar. C) Steric interactions between the heme group and amino acid residues of the /",, polypeptide side chain cause tertiary structural changes in hemoglobin. 1' ® All of the above. 27. Deoxyhemoglobin and oxyhemoglobin, have the following quaternary structural characteristics: A) Deoxyhemoglobin has a larger central cavity than oxyhernoglobin. B) Subunits reorient in the transition from deoxyhemoglobin to oxyhemoglobin and the reverse. C) Quaternary structural changes are the result of tertiary changes brought about by ff" 02 release. \IQJ All of the above. 28. The allosteric effector, 2,3-bisphosphoglycerate (BPG), changes the way 02 is used in the following manner. A) BPG acts to raise the O2 binding affinity of hemoglobin. \ BPfibinds to the iron in hemoglobin through electrostatic interactions. C i BPG binding favors deoxyhemogiobin. D) All the above. 29. The O2 binding affinity of hemoglobin decreases with: A) decrease in pH. ' B) decrease in CO2 concentration. C) increase in pH % increase in CO2 concentration. (in) Both A) and d. 30. The allosteric behavior of O2 binding in hemoglobin results in the following: A) Oxygen binds to all four heme groups of hemoglobin with the same binding affinity as the single heme group in myoglobin. B) Hemoglobin binds O2 in lungs and tissue with the same affinity. C) Hemoglobin binds 02 with increasing affinity as the number of heme groups in hemoglobin binding 02 increases. D) Hemoglobin binds 02 with decreasing affinity as the number of heme groups in hemoglobin binding 02 decreases. @ Both C) and D) 31. Microtubules have the following characteristic(s). I X)? Microtubules are composed of tnbulin orb—dimers Microtubules consist of a single polypeptide chain. C) Microtubules are composed of F—actin.. D) All of the above. E) None of the above. _’ 32. Which of the following is most affected by enzyme concentration? A) K... B) Km C) AG" GEE Vmax E) two of the above 33. Which of the following is true of an enzyme—catalyzed reaction? An enzyme lowers the energy of activation for a reaction. B) An enzyme will lower AS of a reaction. C) An inhibitor will lower the Km of a reaction. D) An activator will raise the Km of a reaction. B) All of the above are false. 34. The steady-state assumption in the derivation of the enzyme-velocity equation is when: A) The total enzyme conCentration is constant over the time frame of the experiment. B) The velocity of the reaction remains constant. @\ The concentration of the enzyme-substrate constant over the time frame of the / experiment. D) The equilibrium constant varies in a constant ratio with time over the time frame of the experiment. E) None of the above are true. 35. An enzyme has been isolated from the liver of a salamander and is found to obey Michaelis-Menten kinetics. At a substrate concentration of 0.01 M, the velocity of the enzyme—catalyzed reaction is found to be 12 umoles/min.. What is the Km value? i ,, 7—1 ,Mjflc/G/Dm, it) 0.0010M [New , i ' ‘ 00025 M 00050 M ) 00075 M E) 00100 M 36. The horizontal intercept of 3 Hanes plot is: A) —1 Nmax f A] B) "Vmax 5:: KW... .r / _ max/Km [A] 37. The following compounds are all substrates of an enzyme that acts on sugars. Which is the most effective substrate? Km Vmax gluccose 0.1 M 0.1 umol/min ribose 0.8 M 0.9 urnol/rnin galactose 0.05 M 0.7 umol/min mannose 0.04 M 0.03 umol/min fructose 0.08 M 0.5 umol/min A) glucose ribose (9)? galactose D) mannose E) fructose 38. A pharmaceutical is found to inhibit a certain enzyme-catalyzed reaction. A plot of NV 39. vs. 1/ [A] in the absence and presence of the enzyme yields the: following plot: M.J I 4.]: n a I yv : The inhibitor is most likely... - I: competitive K‘B uncompetitive C) noncompetitive D) irreversible E) not enough information is given r The presence of an inhibitor is found to lower the Michaelis constant of a substrate. A second inhibitor is found to have no effect on the Km value for the substrate. It is most likely that the second inhibitor is a) competitive r uncompetitive W noncompetitive (1) partial e) irreversible 40. 41. 42. 43. In the plot shown in problem 359, how can you graphically determine the K1- value (that is, the dissociation constant of the inhibitor) A) plot l/v vs‘ l/[I] B); plot v vs. [l1 plot slopes vs. [I] D) plot intercepts vs. [I] E) plot 1/v vs 1/[A] In a multisubstrate reaction involving two substrates and two products, one product is released before the second substrate binds. The enzyme mechanism is most likely A) ordered bi bi B) random bi bi mixed ordered on, random off ping pong bi bi E) abortive In the following biochemical pathway, which compound would you expect to be an inhibitor of enzyme 3. 4 3 /71: 1 2 /YD A—>B———>C F‘s \6‘H A) C ’63» F C) H D) A E) G Which of the following best describes an abortive complex? A) A complex with an inhibitor that can still generate product B) Binding of two or more molecules of inhibitor per enzyme C) Binding of both a competitive and noncompetitive inhibitor at the same time (13) Binding of a substrate and a product on an enzyme at the same time B) None of the above 44, 45. 46. 47'. The regulatory control in which a gene is turned off (thus, the enzyme’s rate of biosynthesis by DNA is lessened) is called A) isozymic B) hysteretic ,3" repression induction E) allosteric A zymo gen is /A)\’].' an inactive enzyme precursor ) an enzyme that catalyzes the exact same reaction as another protein C) a small molecule that acts as a cofactor for an enzyme D) a multi-enzyme complex B) an enzyme found in a membrane The "prime" in AG°’ refers to a number of items, including A) the temperature of the reaction is the physiological temperature (i.e., 98.6°F or \_ 37°C) B) .’ the pH of solution is 7 the concentration of all substances are their physiological concentrations D) the structures of all molecules are their structures at pH 1 E) None of the above The primary reason why ATP has such a large negative AG‘” value for hydrolysis is A) One of the products is resonance stabilized The reactants have a higher degree of hydration C) i The products of a lower electron density ) The net charge on ADP is more negative than on ATP E) Magnesium ions bind tighter to ADP than to ATP r 48. Which of the following is glucose? A ,. _ _/ )CHO (yam C) CHO D) CHO E) CHO 0H 0H "—- 0H OH H0 HO OH HO H Ho HO OH H0 HO HO 0;, Ho * H0 HO OH CHon cHon CHZDH CHZOH [Hwy 49. Which of the following is a nonreducing sugar? A) fructose B) galactose C) n'bose glyceraldehyde / sucrose 50. A disaccharide has been isolated an found to consist of a galactose-linked B1 - 4 to a glucose. The disaccharide is A) maltose B) sucrose C) gentiobiose 1 r 9) cellobiose / lactose --END—— ...
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This note was uploaded on 09/18/2011 for the course BCH 4024 taught by Professor Allison during the Spring '08 term at University of Florida.

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Exam_1_2004_Summer - 497' BCH 4024 INTRODUCTION TO...

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