5-5 CHAPTER 5 REVIEW WKST
1. What is the primary role of enzymes, and how do they accomplish this?
2. What may happen to a catalyst during a specific step of the reaction, and how is it
affected overall?
3. How do catalysts make reactions proceed faster?
4. Why is it important that enzymes are incredibly specific towards their substrates?
5. How can some enzymatic reactions function as control points in metabolism?
Match the enzyme example on the left with the enzyme description on the right.
_____ 6.Aldehyde ferredoxinoxidoreductase
A. Catalyze structure change within single
_____ 7.Phosphoglycerate kinase
molecules
_____ 8.Glycoside hydrolase
B.Catalyze the generation of a double bond
_____ 9.Adenylosuccinatelyase
C. Dehydrogenases, oxidases, peroxidases,
_____ 10. Xylose isomerase
oxygenases, or reductases
_____ 11.DNA ligase
D. Catalyze group-transfer reactions like
the transfer of a phosphoryl group from ATP
E. Catalyze the joining of two substrates
F. Catalyze hydrolysis.
6. A chemical reaction produces 1.30 mol of a product per 500. mL of solution in 1.34
minutes. Calculate the rate (velocity) of the reaction in M/s.
7. Sketch a graph of concentration of product versus time.
[P]
Time 
a. How is the initial velocity calculated?
b. Why use that part of the curve?
8. A series of trials are run that measure the initial velocity of a reaction while increasing
the concentration of the substrate. Sketch a graph that represents the relationship
between the two.
v0
[S]
a. Write the rate law that exemplifies this relationship.
b. How is the rate law constant determined? Why is it determined?
9. Consider the following enzyme-catalyzed reaction with two substrates.
O
OH
OH
+
catechol
1/2 O 2
oxidase
O
+
H2O
a. How is the rate-determining substrate found?
b. Write the rate law for the reaction, recalling that the ½ coefficient for the O2 is for
the overall reaction, not for the rate-determining step of the mechanism.
10. Write an equation that represents a simple enzymatic reaction of converting a substrate to
a product, catalyzed by an enzyme:
a. Which k will determine the reaction efficiency? Why?
11. Write the Michaelis-Menten equation.
a. Why is it named this?
b. What form does it take? Why does it have this form?
c. What does it relate?
12. Write the Michaelis-Menten equation (yes, again).
a. What is Km, and how is it used?
b. Prove that initial velocity becomes independent of substrate concentration when
the substrate concentration is much greater than the Michaelis constant.
c. Prove that the reaction is first order with respect to the substrate when the the
Michaelis constant is much greater than the substrate concentration.
d. Prove that the substrate concentration equals the Michaelis constant when the
initial velocity is equal to one-half of the maximum velocity.
13. Under what conditions does the rate constant become the catalytic constant? How useful
is kcat?
14. Use diagrams to differentiate between sequential and ping-pong mechanisms for
mulitsubstrate reactions.
15. Consider the data collected for an enzyme-catalyzed reaction with two substrates, S1 and
S2.
Experiment
1
2
3
4
5
6
[S1]
50.
100.
50.
50.
25.
10.
Initial Concentration (nM)
[S2]
[E]
50.
50.
50.
50.
150.
50.
50.
100.
25.
25.
10.
?
Initial Rate
(nM/s)
1.02 x 107
2.06 x 107
3.08 x 107
4.12 x 107
?
9.8 x 106
a. Determine the order wrt to each reactant, the overall order, and write the rate law.
b. Determine the rate law constant.
c. Determine the initial reaction rate for experiment 5.
d. Determine the initial concentration of the enzyme in experiment 6.
16. Describe two ways an inhibitor interferes with an enzyme’s activity.
17. What is the difference between reversible and irreversible inhibitors?
18. Compare natural inhibitors and artificial inhibitors.
19. Give examples of substances that are enzyme inhibitors.
20. How does an inhibitor with a low Ki compare to one with a high Ki?
21. Differentiate between classical and nonclassical competitive inhibition. How is the
equation given modified by competitive inhibition?
E + S <=> ES  E + P
22. Differentiate between uncompetitive and noncompetitive inhibition. How is the equation
given modified by these types of inhibition?
E + S <=> ES  E + P
E + S <=> ES  E + P
23. Enzyme inhibition is a powerful tool for probing enzyme _______________ and for
altering it in the treatment of _______________.
24. The pharmaceutical industry uses enzyme inhibition studies to _______________
clinically useful __________. A _______________ occurring enzyme inhibitor is used
as the starting point. Using rational drug design, inhibitors are designed to fit the
__________ site of a target enzyme. The inhibitor is tested on _______________
enzymes first, then in _______________ systems. Problems may arise, and include the
fact that the drug may not __________ the target cell, may be rapidly _______________
to an inactive compound, may be __________ to the host organism, or the target cell may
develop a _______________ to the drug.
25. Demonstrate the general substitution of a lysine residue with an aldehyde by proposing a
mechanism for the process.
Lys
(CH 2)4
N
H
H
O
C
R
H
26. Demonstrate the activity of the nerve gas diisopropylfluorophosphate (DFP) on a serine
residue at chymotrypsin’s active site by proposing a mechanism for the process.
27. Demonstrate the activity of the affinity labelbromohydroxyacetone phosphate on a
glutamate residue by proposing a mechanism for the process.
Glu
(CH 2)2
C
O
O
-
H2C
Br
C
O
CH 2OPO 3
2-
28. Propose a mechanism for the substitution of a deprotonated cysteine side chain with an
alcohol group using peracetic acid.
29. Not only do enzymes __________ up biochemical reactions, they act as control steps in
metabolic pathways by ________________ their catalytic activity!
30. Which controls the regulation of an enzyme more efficiently: Regulating the synthesis or
degradation of an enzyme or reversible modulation? Why?
31. Why do cells need to adjust the rate of their metabolic processes?
32. When does an enzyme become a more active catalyst? Less active catalyst?
33. Allosteric enzymes are changed by metabolic _______________ and _______________,
they bind _______________ and are not _______________ altered, most are
_______________ proteins, and they affect the catalytic _______________, Km.
34. Describe the regulation of the activity of hemoglobin.
35. Describe the regulation of the activity of phosphofructokinase-1.
36. What is the difference between noncovalent modification and covalent modification?
37. Describe the processes of kinases and phoshphatases. Use pyruvate dehydrogenase as an
example.
38. Describe the structure of a multienzyme complex. How does this allow for metabolite
channeling, and how does this help to increase the rate of reaction? Describe two
examples of metabolite channeling.