250+ TOP MCQs on Kinetics of Enzyme Catalysed Reaction – 2 and Answers

Enzyme Technology Quizon “Kinetics of Enzyme Catalysed Reaction – 2”.

1. What does the equation (V_0=frac{V_{max} [S]}{K_m+[S]}) represent?
A. Lineweaver Burk equation
B. Miachelis Menten equation
C. Eadie-Hofstee plot equation
D. Hanes plot equation
Answer: B
Clarification: The equation (V_0=frac{V_{max} [S]}{K_m+[S]}) represents Miachelis Menten equation, where
V₀ = initial velocity, V_max = maximum rate, K_m = Miachelis Menten constant and [S] = substrate concentration.
Line weaker Burk equation, Eadie-Hofstee plot equation and Hanes plot equation are derivatives of Miachelis Menten equation.

2. Which of the following is termed as catalytic efficiency?
A. K_cat
B. K_m
C. K_cat/K_m
D. V_max
Answer: C
Clarification: K_cat/K_m is termed as catalytic efficiency. A high value indicates that the limiting factor of the overall reaction is the collision frequencies between enzyme and substrate molecule, whereas the low value indicates the equilibrium assumption status. K_m and K_cat represent the Miachelis Menten constant and turn over number respectively. V_max is the maximum rate of the reaction catalyzed by enzymes.

3. Which of the following equation is Eadie-Hofstee plot equation?
A. (frac{1}{V_0} = frac{K_m}{V_{max}} frac{1}{[S]}+frac{1}{V_{max}})
B. (V_0=frac{V_{max} [S]}{K_m+[S]})
C. (V_0=K_m frac{V_0}{S_0}+V_{max})
D. (frac{[S_0]}{V_0} = frac{1}{V_{max}} [S_0]+frac{K_m}{V_{max}} )
Answer: C
Clarification: The Lineweaver Burk equation has its own limitations due to the following reasons:
The extrapolation of graph to determine the -1/K_m reaches the edge of the paper such that, the accurate value is unable to calculate.
The -1/K_m value calculated for low substrate concentrations are seemed to be inaccurate for most times.
The linearity of the graph for calculating the -1/K_m value is not clear.
To overcome these, Eadie-Hofstee plot equation was designed. The equation is
(V_0=K_m frac{V_0}{S_0} + V_{max}) where,
V₀ = initial velocity, V_max = maximum rate, K_m = Miachelis Menten constant and [S] = substrate concentration.

4. The equation which is based on reciprocal form of Miachelis Menten equation at constant [Et] level is referred to as ______________
A. Eadie-Hofstee plot equation
B. Eisenthal and Cornish and Bowden plot equation
C. Lineweaver Burk equation
D. Hanes plot equation
Answer: B
Clarification: To overcome certain limitation posed by various plots in determining K_m and V_max, the equation based on reciprocal form of Miachelis Menten equation is referred to as Eisenthal and Cornish and Bowden plot equation. The equation is given by (frac{V_{max}}{V_0} = frac{K_m}{[S_0]}+1) where,
V₀ = initial velocity, V_max = maximum rate, K_m = Miachelis Menten constant and [S] = substrate concentration.
At constant V₀ and S₀, a plot of V_max against K_m will be linear.

5. ______________ is defined as an enzyme molecule’s efficiency to convert maximum substrate molecules into product per unit time.
A. Catalytic efficiency
B. Miachelis Menten constant
C. Turn over number
D. V_max
Answer: C
Clarification: Turn over number is defined as an enzyme molecule’s efficiency to convert maximum substrate molecules into product per unit time. Turn over number is given K_cat and it denotes the catalytic turn over events that happen per unit time. The turn over number for most enzymes ranges from 1 to 10⁵ per second. Miachelis Menten constant is K_m which is calculated as substrate concentration, which results in the half- maximal velocity of the enzymatic reaction. K_cat/K_m is termed as catalytic efficiency. V_max is referred to as maximum rate of an enzyme catalyzed reaction.

6. In the following plot, what does X represent?

A. V_max
B. K_m/V_max
C. –1/K_m
D. S_max
Answer: C
Clarification: The plot represents Lineweaver Burk plot which is devised from the equation, (frac{1}{V_0} = frac{K_m}{V_{max}} frac{1}{[S]}+frac{1}{V_{max}}) where,
V₀ = initial velocity, V_max = maximum rate, K_m = Miachelis Menten constant and [S] = substrate concentration.
According to this plot, the slope gives K_m/V_max, the y intercept gives 1/V_max and the X on the x-intercept gives -1/K_m.

7. What does the following plot represents?

A. Miachelis Menten plot
B. Lineweaver Burk plot
C. Eadie-Hofstee plot
D. Hanes plot
Answer: C
Clarification: Eadie-Hofstee plot is a graphical representation of enzyme kinetics in which reaction velocity is plotted as a function V/[S] which is based on the equation (V_0=K_m frac{V_0}{S_0} + V_{max}) where,
V₀ = initial velocity, V_max = maximum rate, K_m = Miachelis Menten constant and [S] = substrate concentration.
The above plot yields a straight line of slope –K_m, a x-intercept V_max/K_m and an y-intercept V_max.

8. A low K_m value points out a low affinity of an enzyme towards its substrate.
A. True
B. False
Answer: B
Clarification: K_m is defined as the substrate concentration which, results in the half-maximal velocity of the enzyme reaction. The value of K_m varies from one enzyme to other and also affected by certain conditions like pH, temperature, ionic strength, nature of solvent etc. Also, the values of K_m can be different for the mutant forms of enzyme, isoenzyme and even for different substrates catalyzed by the same enzyme. A low value K_m specifies, a high affinity of an enzyme towards its substrate i.e., at even low substrate concentration of substrate an enzyme can initiate the reaction and a high K_m points out a low affinity of an enzyme towards its substrate. Hence the above statement is false.

9. Given an enzyme with K_m of 0.25mM, at what substrate concentration will the velocity of the enzyme reach 1/2 of the V_max? (V_max = 100 mmol/s)
A. 0.5 mM
B. 0.25 mM
C. 0.75 mM
D. 25 mM
Answer: B
Clarification: (V_0 = frac{1}{2} V_{max})
(V_0 = frac{1}{2}*100)
V₀ = 50 mmol/s
(V_0 = frac{V_{max} [S]}{K_m+[S]})
50 = (frac{100 [S]}{0.25+[S]})
(frac{1}{2} = frac{[S]}{0.25+[S]})
0.25+[S]=2[S]
[S]=0.25 mM.

10. An enzyme with a K_m of 5mM has a reaction rate of 100 mmol/min at substrate concentration of 0.25 mmol. What is the maximum reaction rate that this enzyme can achieve when its saturated with substrate?
A. 2100
B. 1500
C. 1900
D. 9000
Answer: A
Clarification: Miachelis Menten equation is given by (V_0=frac{V_{max} [S]}{K_m+[S]})
(V_{max} = frac{V_0 (K_m+[S])}{[S]})
(V_{max} = frac{100 (5+0.25)}{0.25})
(V_{max} = frac{525}{0.25})
(V_{max}) = 2100 mmol/min.

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