Exam_1_2008_Summer

Exam_1_2008_Summer - Lu Which ofthe following is regarded...

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Unformatted text preview: Lu Which ofthe following is regarded as a macroelement in all living organisms? A) vanadium "' m 0 B) scandium t) 2 C) molybdenum D) iodine E) magnesium Which of the following has the highest bond energy? A) C—O B) Si—O C) C~S D) C—H E) C—N Which ofthe following interactions would you expect to be most affected by a large decrease in the dielectric constant of a solution? A) hydrogen bonding B) stacking of aromatic groups C) electrostatic interactions D) disulfide bonds B) van der Waals forces There is a certain metabolic disorder that causes a significant increase in NaCl and KCl concentrations in the blood plasma. Which ofthe following would you expect to be true of this blood plasma compared to the blood plasma of a normal individual? A) There would have to be different types of buffers. B) The osmotic pressure would be larger. C) The dielectric constant would be smaller. D) The freezing point ofthe blood plasma would be higher. E) None ofthe above are true. Homocysteine is an unusual amino acid frequently found in the blood plasma. It has the same structure as cysteine but is one carbon longer (thus, HOOC — CH(NH3+) — CH2 — CH2 — SH). It has pKa values of2.22, 8.87 (for the SH group), and 10.86. You prepare a 100 mL Solution of 0.2 M homocysteine hydrochloride (i.e., the totally protonated form). To this solution, you add 25 mL of 1.0 M KOH. What is the final pH ofthe solution? A) 2.70 B) 6.02 C) 8.39 D) 8.87 a) 9.35 8) 10) One of the most important buffer systems in cells of every living organism is phosphoric acid (H3P04). It has three labile hydrogen atoms and thus three pKa values (2.15, 7.20, and 12.33). lfthe pH value of a cell were 7.5, what fraction ofphosphoric acid would be HP042‘? A) 0.07% B) 33% C) 50% D) 67% E) 93% The chirality of an amino acid results from the fact that its D carbon... A) has no net charge. B) is a carboxylic acid. C) is bonded to four different chemical groups. D) is in the L absolute configuration in naturally occurring proteins. E) is symmetric. The formation of a peptide bond between two amino acids is an example of a(n) reaction. A) cleavage B) condensation C) group transfer D) isomerization E) oxidation reduction Which of the following is correct with reSpect to the amino-acid composition of proteins? A) Larger proteins have a more uniform distribution of amino acids than smaller proteins. B) Proteins contain at least one each of the twenty different standard amino acids. C) Proteins with different functions usually differ significantly in their amino-acid composition. D) Proteins with the same molecular weight have the same amino-acid composition. E) The average molecular weight of an amino acid in a protein increases with the size of the protein. Two amino acids of the standard twenty contain sulfur atoms. They are... A) cysteine and serine. B) cysteine and threonine. C) methionine and cysteine. D) methionine and serine. E) threonine and serine. 1 1) Pauling and Corey’s studies of the peptide bond showed that... A) at pH 7, many different peptide bond conformations are equally probable. B) peptide bonds are essentially planar, with no rotation about the C—N axis. C) peptide bonds in proteins are unusual, and unlike those in small model compounds. D) peptide bond structure is extraordinarily complex. E) primary structure of all proteins is similar, although the secondary and tertiary structure may differ greatly. 12) Which of the following pairs of bonds within a peptide backbone show free rotation around both bonds? A) CuwC and N—Cu B) C=O and NfifiC C) C=O and N——CCl D) N—C and COL—C E) N—COE and Nu+C To answer questions 13—16, refer to the diagram below, which represents part of a protein polypeptide chain: 0 o o 0 H H H H H H H 2H—c|:t—t—~c——N——clza—i—c—r~i——TH—c——N—cu-—c—ot—| CH—CH; rsH—CH3 cH2 CH2 ha is l“: OlZ | OH 13) What amino-acid side—chain is located at position Q11? A) alanine B) valine C) leucine D) isoleucine E) threonine 14) What amino-acid side-chain is located at position Q12? A) alanine B) valine C) leucine D) isoleucine E) threonine 15) What amino-acid side—chain is located at position Q13? A) phenylalanine B) tyrosine C) tryptophan D) histidine E) proline 16) What amino-acid side-chain is located at position Q14? A) phenylalanine B) tyrosine C) tryptophan D) histidine E) proline Refer ONLY to the amino acids listed below to answer questions 17—20: A) methionine B) cysteine C) proline D) lysine E) tryptophan Which amino acid best fits the description below? 17) could form a sait bridge with glutamate 18) causes the greatest conformational constraint on the main—chain of a protein’s fold 19) could form a disulfide bond 20) has the most basic side—chain 21) In the a helix, the hydrogen bonds... A) are roughly parallel to the axis of the helix. B) are roughly perpendicular to the axis of the helix, C) occur mainly between electronegative atoms of the R groups. D) occur only between some of the amino acids of the helix. E) occur only near the amino and carboxyl termini of the helix. 22) In an a helix, the side-chains of the amino-acid residues... A) alternate between the outside and the inside of the helix. B) are found on the outside of the helix spiral. C) cause only right-handed helices to form. D) generate the hydrogen bonds that form the helix. E) stack within the interior of the helix. 23) The major reason that antiparallel B~stranded protein structures are more stable than parallel B—stranded structures is that the latter... A) are in a slightly less extended configuration than antiparallel strands. B) do not have as many disulfide crosslinks between adjacent strands. C) do not stack in sheets as well as antiparallel strands. D) have fewer lateral hydrogen bonds than antiparallel strands. B) have weaker hydrogen bonds laterally between adjacent strands. You may find it useful to refer to the one-letter amino acids code to answer questions 24—27: A: alanine; C: cysteine; D=aspartic acid; E: glutamic acid; F: phenylalanine; G: glycine; H: histidine; I=isoleucine; K: lysine; L: Ieucine; M=methionine; N=asparagine; P: proline; Q: glutamine; R: arginine; S= serine; T= threonine; V: valine; W: tryptophan; Y= tyrosine The po]ypeptide sequences given below (represented by the one—letter code) refer to questions 24—27. A) V—I—F—v—I-T—G-G—A—L-M-E-K-L B) A—V—R—R—P—A—W—T~R—K—T—R—V~T C) A—L—M-L—Q—EwA—L—M—A—M—E—L—M D) A—L—M-E—H—A—P—G—G—EvL—A—H—M E) V»I—F—F—Y—V—T—Y-F—W—I—W-V—F Based on the findings of Chou and Fasman, which of the above polypeptide sequences would most likely occur in a(n)... 24) a-llfilix? 25) B—strand? 26) (it-helix turn a-helix? 27') B—strand turn (it-helix? To answer questions 28—31, please refer to the Ramachandran plot below. +180 Region I 120 E 60 Region 11 cu L- 81 0 Region II] E ‘9 ‘“ 50 Region IV - 120 - 180 - 180 0 +180 ch (degrees) Consider the following proteins Protein A B C D r“ in: x " ‘ ' 1 “‘7‘; i x “‘1 ,.‘ f "f 47 r?"* E (5::é1fa ‘17? / «.- i .4 1“?“ ¢ I :.\ \La 1’): t k .1; If < b 15‘,» / flagging r - '- r“.i‘, F t- if“ M s 1397:: I 5‘ h I“, \V M. ‘I /\ “33(153 ‘x. 3»- ?gg'l: l* i ‘ \‘Ln [Eleni l:"‘—,J/. t wt: If / M.- x k, 28) In which region of the Ramachandran plot would you most likely expect to plot psi and pin angles for the amino acid in protein A? A) mainly region I B) mainly region 11 C) mainly region 111 D) mainly region IV E) region I and II 29) In which region of the Ramachandran plot would you most likely expect to plot psi and phi angles for the amino acid in protein B? A) region 1 and II B) region I and III C) region I and IV D) region 11 and IV E) region 111 and IV 30) In which region of the Ramachandran plot would you most likely expect to plot psi and phi angles for the amino acid in protein C? A) region I and H B) region I and III C) region land IV D) region Hanle E) region 111 and IV 31) In which region ofthe Ramachandran plot would you most likely expect to plot psi and phi angles for the amino acid in protein A? A) mainly region 1 B) mainly region II C) mainly region HI D) mainly region IV E) region 1 and Il -—-——————-—————-—-———————_..__—___——__—__ 32. Which of the following is most affected by the total enzyme concentration? A) Km B) individual rate constants C) Keq D) Vmax E) none ofthe above 33. The steady—state assumption is key in the derivation of the Michaelis—Menten equation. Which arrow in which progress—curve below best depicts the steady—state assumption? I 9'] 34. 35. 36. 37. 38. An enzyme catalyzes the conversion of L—alanine to D—alanine. It has a Vmax value of 18 tunoles/rnin, and, when the substrate substrate concentration is 3.2 HM, the velocity is 7.3 “moles/min. What is the Km value? a) 2.13 MM b) 3.84 uM c) 4.69 uM d) 6.40 0M 6) 9.00 0M What is the horizontal intercept in a Hanes plot? [A] V a) 'Krn / Vmax [A] b) —l xv"... 0) -Km/ d) ' Vmax 6) ' Vmax 1f the substrate concentration is four times larger than the Km value, the velocity of the of the Vmax value. enzyme-catalyzed reaction will be equal to a) 50% b) 67% c) 80% d) l 00% e) undetermined An enzyme catalyzes the oxidation of several amino acids. Of the amino acids shown below, which is the most efficient substrate? Vmax l urnol/min 3 umol / min 5 umol / min 8 umol / min 12 umol / min a) alanine b) isoleucine c) methionine d) tyrosine e) tryptophan Km 0.001 M 0.002 M 0.02 M 0.05 M 0.01 M An inhibitor binds to both the free enzyme and the enzyme-substrate complex. The inhibitor is most likely a) competitive b) noncompetitive c) uncompetitive d) hysteretic e) none ofthe above 39. Which ofthe following plots refers to an uncompetitive inhibjmr? noI E) Na-ne 070 fie agave, 40. 41. 42. 44. 45. How would an investigator graphically obtain the Ki value for a competitive inhibitor? A) B) C) D) E) plot l/V vs. 1 / [I] plot vertical intercepts vs. 1 / [l] plot slopes vs. 1 /[l] plot Vmax/ [A] vs. [I] plot slopes vs. [I] A particular enzyme is inactive until a sequence of amino acids is cleaved from its primary structure. This inactive protein is called A) B) C) D) B) an isozyme. a zymogen. a hysteretic protein. a cooperative protein. none of the above Which of the following describes an abortive complex? A) B) C) D) E) a complex of two or more proteins an enzyme that can undergo feedback inhibition and feed—forward activation an enzyme binding a substrate and a product at the same time any ping—pong enzyme none of the above An enzyme is showo to exhibit sigmoidal (i.e., cooperative or non—hyperbolic) kinetics. The substrate binds to the enzyme after it has undergone a slow conformational change. The enzyme is most likely A) B) C) D) E) a Monod-Wyman—Changeaux protein. a hysteretic protein. a feed—forward protein. a zymogen. a Koshland-Nemethy—Filmer protein. In the cell, ATP typically forms a 1:1 complex with A) B) C) D) E) ribose. hemoglobin. Na+ Mg+ creatine The [36" value for the hydrolysis of ATP becomes more negative with A) B) C) D) E) ATP concentration. elevated pH. ADP concentration. lower temperature. none of the above 46. 47. 48. 49. Which of the following best describes an entropically driven reaction? (Remember AG=AH—TAS) AG AH A) >0 >0 B) <0 <0 C) <0 <0 D) >0 <0 E) <0 >0 Which ofthe following sugars is a ketose‘? A) fructose B) glucose C) ribose D) xylose E) sucrose Which of the following disaccharicles contains galactose? A) sucrose B) maltose C) lactose D) gentiobiose E) cellobiose Which of the following contains [31 9 4 linkages? A) amylose B) amylop ectin C) cellulose D) sucrose E) maltose On ’1")? éfiCk ’7} of each other? epimers of the following sugars shown below are Which two 50. HH OHHWOW Uul____nh® .ICICICICLL Cu... .# 23454 mmmmm aaaaa ...
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This note was uploaded on 06/07/2011 for the course BCH 4024 taught by Professor Allison during the Fall '08 term at University of Florida.

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Exam_1_2008_Summer - Lu Which ofthe following is regarded...

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