1. Which of the following assumption was not made in rapid equilibrium model?
a) Flexible nature of enzymes
b) [S] >> [E]
c) [E]+[S]\(\rightleftharpoons\)[ES]
d) It is the initial substrate concentration [So] that determines efficacy of an enzyme to mediate a reaction
Explanation: The flexible nature of enzymes was not dealt by lock and key model, but the induced fit model. This model dealt with change in shape after enzyme substrate interaction. The following assumptions were made in rapid equilibrium model:
* The substrate concentration will always be higher than enzyme concentration. [E] >> [S]
* An equilibrium state is assumed between reactants and products. [E]+[S]\(\rightleftharpoons\)[ES]
* It is the initial substrate concentration [So] that determines the efficacy of an enzyme to mediate a reaction.
2. Which of these is referred to as Kcat?
a) Miachelis Menten constant
b) Catalytic efficiency
c) Substrate concentration
d) Turn over number
Explanation: Kcat is referred to as turn over number which denotes the number of catalytic turn over events that happens per unit time. Catalytic efficiency is given by Kcat/Km. Miachelis Menten constant is given by Km. Substrate concentration is the amount substrate used in an enzyme catalyzed reaction.
3. What does the following equation represent?
\(\frac{1}{V_0} = \frac{K_m}{V_{max}} \frac{1}{[S]}+\frac{1}{V_{max}}\)
a) Eadie-Hofstee plot equation
b) Lineweaver Burk equation
b) Miachelis Menten equation
b) Hanes plot equation
Explanation: The Miachelis Menten equation is proved to be unsatisfactory for the following reasons:
The graph proposed is not following a proper mathematical model.
The graph is following a tangent model and hence it is difficult to calculate an exact Km and Vmax.
Hence Lineweaver and Burk came up with a suitable solution to solve this problem. The equation
\(\frac{1}{V_0} = \frac{K_m}{V_{max}} \frac{1}{[S]}+\frac{1}{V_{max}}\) represents Lineweaver Burk equation where,
V0 = initial velocity, Vmax = maximum rate, Km = Miachelis Menten constant and [S] = substrate concentration.
4. Which of the following is based on rearrangement of Lineweaver Burk plot equation by multiplication of [So] factor?
a) Hanes plot equation
b) Eadie-Hofstee plot equation
c) Miachelis Menten equation
d) Eisenthal and Cornish and Bowden plot equation
Explanation: Hanes plot equation is based on rearrangement of the Lineweaver Burk plot equation by multiplication of [S0] factor and is given by \(\frac{[S_0]}{V_0} = \frac{1}{V_{max}} [S_0]+\frac{K_m}{V_{max}}\)
where,
V0 = initial velocity, Vmax = maximum rate, Km = Miachelis Menten constant and [S] = substrate concentration.
The graphical representation of [S0]/V0 versus [S0] is called the Hanes plot. One of the drawbacks of this approach is that neither the ordinate nor the abscissa represents independent variable, both are dependent on substrate concentration.
5. Miachelis Menten model is also referred to as “rapid equilibrium model”.
a) True
b) False
Explanation: The main difference between Henri and Miachelis Menten model is that Miachelis and Menten did a strong experimental work to prove that any enzyme catalyzing single substrate reaction will possess a hyperbolic curve. The unique feature of this model is assumption of rapid equilibrium between reactants and ES complex, where the ES complex will slowly decompose to form free enzyme and products. Hence it is appropriate to term this model as “rapid equilibrium model”. Hence the above statement is true.
6. ___________ is defined as the enzyme’s binding efficiency with its appropriate substrate through optimized multiple non-covalent interactions.
a) Km
b) Kcat
c) Catalytic efficiency
d) Vmax
Explanation: Km is defined as the enzyme’s binding efficiency with its appropriate substrate through optimized multiple non-covalent interactions. Km is also referred to as the substrate concentration at which the reaction occurs at half of the maximum rate. Kcat is referred to as turnover number that denotes the number of catalytic turn over events that happen per unit time. Catalytic efficiency is referred to Kcat/Km. The high value of this indicates collision frequencies between enzyme and substrate molecule and low value indicates the equilibrium assumption status. Vmax is the maximum rate of the reaction.
7. 4*107: Catalase :: 25: ___________
a) Protease
b) Amylase
c) Glucose isomerase
d) Creatinine kinase
Explanation: 4*107 is the value of catalytic efficiency of catalase. Catalytic efficiency is referred to as Kcat/Km. High value indicates that the collision frequencies between enzyme and substrate molecule and low value indicates that the equilibrium assumption status. As 4*107 M-1s-1 is the value of catalytic varies from less than 1 M-1s-1 to greater than 108 M-1s-1.
8. What is the ratio of V0/Vmax when [S] = 10Km?
a) 1/2
b) 10/11
c) 4/5
d) 5/6
Explanation: Miachelis Menten equation is given by \(V_0=\frac{V_{max} [S]}{K_m+[S]}\)
Rearranging, \(\frac{V_0}{V_{max}} = \frac{[S]}{[S]+K_m}\)
\(\frac{V_0}{V_{max}} = \frac{10K_m}{10K_m+K_m}\)
\(\frac{V_0}{V_{max}} = \frac{10 K_m}{11 K_m}\)
\(\frac{V_0}{V_{max}} = \frac{10}{11}\)
9. The presence of enzyme in the sample can be detected by _________________
a) gel exclusion chromatography
b) affinity chromatography
c) ion exchange chromatography
d) thin layer chromatography (TLC)
Explanation: Enzyme which have been clarified and concentrated can be detected by thin layer chromatography. Gel exclusion, affinity and ion-exchange chromatography are used for purification of enzymes based on the property of the enzyme.
10. The method which relies on differences in partitioning behavior between a flowing mobile phase and a stationary phase to separate the components in a mixture is referred to as _________________
a) homogenization
b) dialysis
c) chromatography
d) ultrafiltration
Explanation: In chromatography, there is a column which holds the stationary phase and mobile phase carrying the sample pass through it. The components in the sample which partition strongly in the stationary phase spend greater time in the column and get separated from the components which stay in the mobile and pass through the column faster. As the components get eluted, they may be quantified by a detector or collected for further analysis. Homogenization is a physical technique to separate out the cell components into the medium. Dialysis and ultrafiltration are the steps involved in enzyme purification.