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Midterm

F05_BIOC-2580_Midterm.pdf

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Department
Biochemistry
Course
BIOC 2580
Professor
Enoka Wijekoon
Semester
Fall

Description
Name: _____WHITE_______________ Student Number: ____________________ Answer the following questions on the computer scoring sheet. 1 mark each 1. Which of the following amino acids would have the highest relative mobilfty R in normal thin layer chromatography? A) Lys B) Leu C) Asn D) Thr E) Asp 1) A B C D E least polar 2. Which of the following amino acids is most likely to be found on the outer surface of a properly folded protein? A) Ile B) Phe C) Asp D) Val E) Met 2) A B C D E most polar 3. Which of the following amino acids prefers β-sheet secondary structure? A) Ile B) Pro C) Ala D) Gly E) Glu 3) A B C D E branched on β-carbon 4. Which of the following amino acids can donate H-bonds from its side chain? A) Phe B) Gln C) Ala D) Leu E) Gly 4) A B C D E O=C-NH 2n side chain 5. Identify the amino acid drawn on the right: A) Asparagine B) Arginine C) Threonine D) Glutamine E) Lysine 5) A B C D E 6. Which of the following statements correctly describes why Ninhydrin is used in amino acid and peptide analysis? A) to detect amino acids by a color reaction B) to identify the N-terminal amino acid C) as the product of the cyclization step in Edman's reaction D) to reduce disulphide bonds E) to cut the peptide chain at methionine 6) A B C D E 7. By what factor does a typical enzyme speed up reaction rate compared to uncatalyzed reaction? A) 10 fold B) 100 fold C) 1000 fold D) 10000 fold E) 1000000000 fold 7) A B C D E 8. Which of the following represent the catalytic triad of chymotrypsin? A) Phe, Tyr and Trp B) His, Lysand Arg C) Asp, His and Ser D) Gly, Ser and Phe E) Ala, Gly and Ser 8) A B C D E 9. In the structure of the α-helix, which of the following pairs of groups is linked together by a hydrogen bond? A) α-NH of amino acid 1 to α-CO of amino acid 3 B) α-NH of amino acid 1 to α-CO of amino acid 4 C) α-NH of amino acid 1 to α-CO of amino acid 5 D) α-CO of amino acid 1 to α-NH of amino acid 4 E) α α-CO of amino acid 1 to α α-NH of amino acid 5 9) A B C D E 10. What initial reaction velocity o is observed if substrate concentration in an enzyme reaction is 0.5 × M and Vmax is 2.4 × 10 mol L min ?-1 A) 1.2 × 10 mol L min . B) 6.0 × 10 mol L min . -6 -1 -1 -7 -1 -1 C) 2.4 × 10mol L min . D) 8.0 × 10 mol L min . E) 1.6 × 10 mol L min . 1/3 V 10)A B C D E max 11. What substrate concentration, expressed as a multiple of M, must be present when an enzyme reaction is observed to have an initial rote v = 0.maxV .? A) [S] = 0.25 × M B) [S] = 0.75 × M C) [S] = 1.33 ×MK D) [S] = 3.0 × K M E) [S] = 4.0 × M 11)A B C D E 12. The plot at right represents initial rate of an enzyme catalyzed reaction as afunction of [S]. Vo Why does the curve level off towards the right? [S] A) Substrate is running out. B) Affinity for substrate is low and it's not binding to the enzyme C) Product is accumulating and causing the reverse reaction to occur D) All the available enzyme is fully occupied with substrate E) An inhibitor must be present and is slowing down the reaction 12)A B C D E 13. What is the net charge of the following peptide at pH 5.0? -0.5 +1 +1 +Ala-Cys-Leu-Ser-Glu-Lys-Met-Tyr-His-Val-Thr – A) + 0.5 B) +1 C) +1.5 D) +2 E) +2.5 13)A B C D E 14. Which of the following represents the major energy contribution that causes a typical protein to fold in its usual tertiary structure? A) Disulfide bonds B) Hydrogen bonds C) Ion pairs D) Salt bridges E) Hydrophobic and non-polar interactions 14)A B C D E 15) Which of the following best describes the role of the oxyanion hole in chymotrypsin? + A) Its negative charge helps His 57 capture H and become positive B) It binds the substrate C=O group in a position that helps form the transition state C) It makes a better nucleophile for the reaction D) It is responsible for recognizing aromatic amino acids as the targets for hydrolysis E) It is responsible for recognizing positively charged amino acids for hydrolysi15)A B C D E 16) How are K aMd V maxdeduced from a Woolf-Hanes plot? A) K Ms the slope andmaxs the y intercept B) K Ms the y intercept amaxis the slope C) –K is Mhe x intercept and 1/V max is the slope D) –1/K Ms the x intercept anmaxis the slope E) –1/KMis the x intercept anmaxis the y intercept 16)A B C D E 17) What are the characteristics effects of acompetitive inhibitor on enzyme kinetics? A) K Mecreases and Vmaxs unchanged B) K inMreases and V max is unchanged C) K Ms unchanged and maxis decreased D) K Ms unchanged and maxincreases E) K Mecreases and maxis increased 17)A B C D E 18) Which of the following statements about a noncompetitive inhibitor is NOT true? A) Substrate can bind to the EI complex B) Inhibitor can bind to the ES complex C) Kiis the concentration of inhibitor causing rate of catalysis to decrease by 50% D) Very high [S] can overcome the effect of the inhibitor E) The inhibitor and the substrate do not share the same binding site 18)A B C D E 4 -1 -1 19) The extinction coefficient of adenosine monophosphate is 1.51 × 10 L mol cm at 260 nm. If a sample 1.00 cm thick has absorbance 0.604 at 260 nm, what is the concentration of adenosine monophosphate? -5 A) 4.00 × 10 mol/L B) 4.00 × 10 mol/L C) 1.04 × 10 mol/L D) 2.5 × 10mol/L E) 9.6 × 10 mol/L 19)A B C D E 20) Which of the following definitions describes turnover number of an enzyme? A) moles per liter of substrate converted to product per second B) moles of substrate converted per second C) moles of substrate converted per mole of enzyme per second D) molecules of substrate converted per molecule of enzyme per second E) both C) and D) are correct 20)A B C D E Name _____ white ____________________ 21 a). How does chymotrypsin bind and recognize aromatic amino acids Phe, Tyr and Trp, but not smaller non polar amino acids such as Ala or Val? (no need to discuss catalytic mechanism) 2 marks ½ mark each point Selected side chain fits in a nonpolar pocket in the chymotrypsin Pocket is large, to fit aromatic amino acids benzene ring
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