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4.2 Kinetics β Test 1
Q1. Site-directed mutagenesis gives WT (kcat=77 sβ»ΒΉ, KM=20 Β΅M), M1 (70, 17), M2 (0.15, 20), M3 (0.001, 18). Which has the highest catalytic efficiency?β Mutant 1
Q2. WT enzyme: kcat=0.37 sβ»ΒΉ, KM=3.4 mM. Mutant: kcat=1.1 sβ»ΒΉ, KM=0.7 mM. Approximate fold increase in catalytic efficiency?β 14
Q3. Enzyme multiplicity regulates amino acid biosynthesis. A correct example is:β Chorismic acid mutase and Aldolase
Q4. Which enzyme form is more active?β Deadenylated glutamine synthetase
Q5. Glutamine synthetase is regulated reversibly by:β Adenylylation and deadenylylation
Q6. Most metabolic enzymes operate in vivo:β Below saturation and below Km
Q7. To estimate substrate concentration in an assay, the enzyme should preferably have a:β Km above the substrate concentration
Q8. In a LineweaverβBurk plot, the Y-axis data are expressed as:β 1/V
Q9. For MichaelisβMenten kinetics, if KM = 5 mM and vβ = 12.5 Β΅mol/(mLΒ·s) at [S] = 5 mM, what is Vmax?β 25
Q10. A lipase has kcat = 25.0 sβ»ΒΉ and KM = 0.0048 M. At what [S] does it show one-fifth of its maximum rate?β 1.2 Γ 10β»Β³ M
Q11. Vmax for an enzyme following simple MichaelisβMenten kinetics, if vβ = 2 Β΅mol minβ»ΒΉ at [S] = 10 KM?β 2.2 Β΅mol minβ»ΒΉ
Q12. On a MichaelisβMenten plot, the curve plateaus and does not rise further on adding substrate because:β The active site is saturated with substrate
Q13. Which one is a tandem enzyme?β Phosphofructokinase 2
Q14. Efficiency of an enzyme is best measured in terms of:β Kcat/Km
Q15. Which is a unit of catalytic efficiency (kcat/KM) of an enzyme?β minβ»ΒΉ Mβ»ΒΉ
Q16. Which correctly shows the EadieβHofstee plot?β V vs V/S
Q17. In EadieβHofstee plots, the X-intercept and Y-intercept are respectively:β Vmax and Vmax/Km
Q18. Two strains: Bsyrup (KM 100 mM, Vmax 1000) and Bsoil (KM 10 mM, Vmax 100), assayed at 10/100/1000 mM glucose. Which statement is correct?β Bsoil higher Vo at 10 mM than Bsyrup
Q19. Which is true for enzyme-catalysed reactions?β Vmax can never be achieved
Q20. At substrate concentrations much lower than KM, reaction velocity is:β Directly proportional to [S]
Q21. Which is obtained by multiplying the LineweaverβBurk equation by [Sβ]?β Hanes plot equation
4.2 Kinetics β Test 2
Q22. For the HanesβWoolf plot ([S] on X, [S]/v on Y), which statement is correct?β The X-intercept is βKm
Q23. Cooperative ligand binding is described quantitatively by the:β Hill equation
Q24. If the product is formed in an exponential pattern, the initial velocity can be determined by applying:β Logarithmic equation
Q25. The SI unit for enzyme activity is the katal. One katal equals:β 6 Γ 10β· IU
Q26. One katal is (repeat):β 6 Γ 10β· IU
Q27. In enzyme kinetics, the rate constant kcat refers to:β Turnover number
Q28. The unit of kcat of an enzyme cannot be:β sβ»ΒΉ
Q29. KM is characteristic of an enzymeβsubstrate pair and is independent of enzyme amount, but Vmax varies with the:β Amount of enzyme used
Q30. Glucokinase (kcat 600 sβ»ΒΉ) with Et = 20 Β΅mol and [S] = 40 Β΅mol gives vβ = 9.6 Β΅mol/s. The KM is:β 10 Β΅moles
Q31. A protein kinase hydrolyses substrate (0.03 mmol/L) at vβ = 1.5Γ10β»Β³ mmol/L/min with Vmax = 4.5Γ10β»Β³ mmol/L/min. KM is:β 0.06
Q32. A LineweaverβBurk plot has slope 0.095 s and Y-intercept 0.0126 sΒ·Β΅Mβ»ΒΉ. The KM (in mM) is:β 7.54Γ10β»Β³
Q33. For KM, which statements hold? (a) High KM = high affinity; (b) KM indicates enzymeβsubstrate affinity; (c) KM defines the [S] for effective catalysis.β b and c
Q34. The MichaelisβMenten constant KM is:β Numerically equal to the [S] giving half-maximal velocity
Q35. The Michaelis constant KM is:β Numerically equal to the [S] giving half-maximal velocity
Q36. A low KM value indicates:β High substrate affinity
Q37. Identify the true statement about KM:β Km is independent of enzyme concentration
Q38. The relationship between KM and Kd in an enzyme-catalysed reaction is:β Km is usually more than Kd
Q39. The substrate KM in an enzyme-catalysed reaction:β Is never less than Kd
Q40. If a 1/v vs 1/[S] plot is linear, this indicates:β A pre-equilibration
Q41. For enzymes obeying MichaelisβMenten, a 1/vβ versus 1/[S] plot is the:β LineweaverβBurk plot
Q42. When [S] = 0.5ΓKM, the velocity vβ is about:β 0.3ΓVmax
4.2 Kinetics β Test 3
Q43. For an enzyme following MichaelisβMenten, when [S] = KM, v equals:β 0.5 Vmax
Q44. For MichaelisβMenten when [S] βͺ KM, which holds?β vβ = (Vmax/Km)[S]
Q45. For an enzyme's MichaelisβMenten equation when [S] is very low compared with KM:β vβ = (Vmax/Km)[S]
Q46. At [S] = 2KM, the percentage of Vmax (using v = Vmax/(1+KM/[S])) is:β 66.70%
Q47. An enzyme has KM = 1 mM and Vmax = 5 nM/s. The reaction velocity at [S] = 0.25 mM is:β 1 nM/s
Q48. A lipase has kcat = 25.0 sβ»ΒΉ and KM = 0.0048 M. At what [S] does it show one-fifth of its maximum rate?β 1.2 Γ 10β»Β³ M
Q49. Voβ[S] relationship for an enzyme following MichaelisβMenten has the shape of a:β Rectangular hyperbola
Q50. An enzyme shows v = 10 Β΅mol/min when [S] = KM. Its Vmax is:β 20 Β΅mol/min
Q51. When [S] = 0.5ΓKM, the velocity vβ is about:β 0.3ΓVmax
Q52. When velocity is plotted against substrate concentration, it shows a:β Hyperbolic curve
Q53. The rate-determining step of the MichaelisβMenten mechanism is:β The product formation step
Q54. A pure 47 kDa monomeric kinase has specific activity 200 U/mg. 50 Β΅g is found in 100 mL buffer, assayed at saturating substrate. The reaction rate (1 U = 1 Β΅mol/min) is:β 1 Γ 10β»β΄ M/min
Q55. Which property of an enzyme is responsible for saturation behaviour (a maximum rate insensitive to rising [S])?β The enzyme has a fixed number of active sites
Q56. 'Specific activity' differs from 'activity' in that specific activity:β Is the activity (units) per milligram of protein
Q57. An uninduced culture has 228 units of Ξ²-galactosidase per mL and 43 Β΅g protein per mL. The specific activity is:β 5302
Q58. Which might be the units for specific activity of an enzyme?β Β΅mol minβ»ΒΉ mgβ»ΒΉ
Q59. The specific activity of an enzyme is reported in:β Units per milligram
Q60. Which might be the units for specific activity of an enzyme?β Β΅mol minβ»ΒΉ mgβ»ΒΉ
Q61. The MichaelisβMenten equation relates the rate of an enzyme reaction to:β Substrate concentration
Q62. Turnover numbers: E1 = 150 sβ»ΒΉ, E2 = 15 sβ»ΒΉ. This means:β Velocities at saturating substrate could be equal if [E2] = 10Γ[E1]
Q63. Which parameter changes upon doubling enzyme concentration?β Vmax
Q64. At substrate concentrations where the rate reaches Vmax, the reaction follows ___ kinetics.β Zero order