NPTEL – Biotechnology - Systems Biology
Michaelis Menten Kinetics- Enzyme Kinetics,
Binding and Cooperativity
Dr. M. Vijayalakshmi
School of Chemical and Biotechnology
SASTRA University
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Table of Contents
1 QUESTIONS ...................................................................................................... 3
2 ANSWERS ........................................................................................................ 8
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1 Questions
1. The major limitation of MM kinetic arises from the fact that its kinetics is derived
from _______.
2. Enzymes require cofactors for their functioning and most of the cofactors are
vitamins. Identify which of the following statements is not true.
a) Vitamins are modified by the body to form co enzymes
b) Vitamins exist in water soluble and water insoluble forms
c) Potassium, nickel and zinc are classes of vitamins
3. Rate curves of allosteric enzymes follow
a) MM kinetics
b) Sigmoidal kinetics
c) Hyperbolic kinetics
4. Which of the following model of allosteric regulation discusses conformational
changes of a single enzyme.
a) Cooperative binding model
b) Transition state model
c) Sequential model
5. Consider an irreversible reaction. If a reactant in such a reaction decreases by 8
fold from its initial state during a time interval of 12 minutes. Calculate the half life
of the reactant in the reaction
a) 12 minutes
b) 2 minutes
c) 1.5 minutes
d) 4 minutes
6. Consider an enzyme catalysed reaction with a single substrate. Under conditions
for MM kinetics, if the initial velocity is plotted against the initial substrate
concentration, one finds an increase with increase in S. But the plot eventually
levels off and approaches the maximum. This is because
a) The substrate is depleted
b) The reverse reaction increases
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c) All enzymes displays saturation kinetics
7. Proteolytic cleavage of zymogens to produce active enzymes is a __________
reaction.
a) Reversible
b) Irreversible
c) Random
8. Which of the following statements is true for an enzymatic reaction following MM
kinetics
K1
K2
E+S----->ES---->E+P
K -1
a) V0 is proportional to K1
b) Initial velocity V0 is maximum at high substrate concentrations
c) The rate constant at high substrate concentration is K2/KM
9. The concentration of 2, 3 –BPG increases during high altitude adaptation. How is
the oxygen binding curve of haemoglobin altered?
a) The sigmoidal oxygen binding curve shifts to the left.
b) The sigmoidal oxygen binding curve shifts to the right.
c) The sigmoidal oxygen binding curve is hyperbolic.
10. Look at the free energy diagram given below. Which of the following is true about
the diagram.
a) Delta G1 determines the equilibrium constant
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NPTEL – Biotechnology - Systems Biology
b) A catalyst accelerates the reaction by decreasing delta G1 and delta G2
c) Delta G3 determines the rate of the reaction.
11. Look at the following table of enzyme kinetics
V0 (µ mol/min)
[S] mM
167
1.6
251
4
333
8
375
12
498
2000
1. Approximate KM for the enzyme
a) 2000 mM
b) 4 mM
c) 6mM
2. For [S] = 1mM, V0 is
a) 200 mM
b) 100 µ mol/min
c) 100mM
12. When do ligands show positive cooperativity towards the enzymes and when do
they show negative cooperativity?
13. Hill coefficients range from _________ during positive cooperativity, while
negative cooperativity have hill coefficients ________.
14. Under what condition does competitive inhibition occur in an enzymatic reaction?
15. The
inhibition
of
DHFR
by
methotrexate
to
convert
dihydrofolate
to
tetrahydrofolate is a typical example of ___________.
16. What are the conditions in which un-competitive inhibition occurs in an enzymatic
reaction?
17. What are the conditions in which non-competitive inhibition occurs in an
enzymatic reaction?
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18. How does the concentration of the substrate change during pre steady state and
steady state of a reaction
19. What is the turn over number refer to in enzyme kinetics?
20. The initial velocity, vo, of an enzyme catalyzed reaction reaches Vmax when
______
21. An un-competitive inhibitor of an enzyme usually binds to ______ and _______
Vmax.
22. Once a ligand dissociation constant (Kd) has been determined it is possible to
calculate _______
a) ligand binding constant (Ka)
b) ΔG for the binding interaction
c) Enthalpy of the binding interaction
d) Concentration of ligand
23. Which does not influence the enzyme activity?
a) pH
b) Temperature
c) Substrate concentration
d) Product degradation
24. In a reaction, substrate and product are in equilibrium. Addition of enzyme to this
mixture will ________
a) More product will be formed
b) Free energy of reaction changes
c) Reaction will remain in equilibrium
25. In enzyme catalysed reactions, _________
a) Reaction is faster that that without the presence of enzyme
b) Free energy change is opposite to that without the presence of enzyme
c) Reaction is always in chemical equilibrium
d) All a, b and c are correct
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26. One can overcome ________ in an enzymatic reaction by increasing the
substrate concentration
a) Allosteric inhibition
b) competitive inhibition
c) Non-competitive inhibition
d) saturation of enzyme
27. A non competitive inhibitor decreases the rate of reaction by _____
a) Binding to active site
b) Changing shape of reactant
c) Changing free energy of reaction
d) decreasing activation energy of reaction
28. Advantage of Adair model over Hill model _________
29. The distance between the two straight lines of Hill plot gives
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NPTEL – Biotechnology - Systems Biology
2 Answers
1. Law of mass action , rate equation , chemical equilibrium
2. c) Potassium, nickel and zinc are classes of vitamins
3. b) Sigmoidal kinetics
4. c) Sequential model
5. d) 4 minutes
6. c) All enzymes displays saturation kinetics
7. b) Irreversible
8. b) Initial velocity V0 is maximum at high substrate concentrations
9. b) The sigmoidal oxygen binding curve shifts to the right.
10. b) A catalyst accelerates the reaction by decreasing delta G1 and delta G2
11. 1. b) 4 mM
2. b) 100 µ mol/min
12. Positive cooperativity is shown when the binding of the first ligand facilitates the
binding of the other on reverse conditions it shows negative cooperativity.
13. 1 to n, less than 1.
14. When the inhibitor is highly homologous to the substrate molecule and competes
with the substrate to bind to the free enzyme.
15. Competitive inhibition.
16. When the inhibitor does not bind to the free enzyme but binds to the already
formed enzyme substrate complex making the complex inactive.
17. When the inhibitor binds to a different site in the enzyme.
18. At the pre steady state the substrate concentration is more than the enzyme
concentration. The concentration of the enzyme substrate complex increases
with time as the reaction proceeds and reaches a steady state. Once the steady
state is reached the concentration does not change with time.
19. The number of molecules of substrate converted into product at a unit of time by
a single enzyme molecule.
20. [s] = Km
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21. ES complex, decreases
22. a , b and d
23. d) Product degradation
24. c) Reaction will remain in equilibrium
25. a) Reaction is faster that that without the presence of enzyme
26. b) Competitive inhibition
27. b) Changing shape of reactant
28. 1. Number of binding sites can’t be obtained by hill equation.
2. Hill equation does not describe the binding relationships
29. Energy difference between the R and T states
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