CHEMISTRY
OF ENZYMES
1. Without exception, all enzymes belong to which
class of biological molecules?
A.
Carbohydrates
B. Lipids
C. Nucleic
acids
D. Proteins
Correct Answer: D. Proteins
2. What is the effect of minor alterations in the
precise conformational structure of an enzyme's folded polypeptide chains?
A. Increased
specificity
B. Loss of
activity
C. Increased
substrate binding
D. No
significant effect
Correct Answer: B. Loss of activity
3. In an enzyme-catalyzed reaction, what term is used
for the substance upon which an enzyme acts?
A. End product
B. Catalyst
C. Substrate
D. Coenzyme
Correct Answer: C. Substrate
4. Which key metabolic role do enzymes fulfill in
living organisms?
A. They slow
down metabolic reactions.
B. They are
consumed during the catalytic process.
C. They
accelerate metabolic reactions.
D. They
synthesize genetic material.
Correct Answer: C. They accelerate metabolic reactions.
5. What are the end products when amylase acts on
starch?
A. Glucose and
galactose
B. Maltose and
dextrins
C. Amino acids
and peptides
D. Fatty acids
and glycerol
Correct Answer: B. Maltose and dextrins
6. Due to the catalytic functions of enzymes, all
physiologic processes occur in what manner within the cell?
A. Random,
uncontrolled manner
B. Ordered,
regulated manner
C. Slow,
inefficient manner
D. Independent
of pH
Correct Answer: B. Ordered, regulated
manner
7. In liver cirrhosis, the inability of cells to
synthesize key enzymes responsible for converting ammonia into urea leads to
which condition?
A. Glucose
deficiency
B. Ammonia
intoxication
C. Acidosis
D. Increased
absorption
Correct Answer: B. Ammonia intoxication
8. Measurement of intracellular enzymes released into
the blood following severe tissue injury provides physicians with what type of
information?
A. Only
curative information
B. Only
preventative information
C. Diagnostic
and prognostic information
D. Only
nutritional requirements
Correct Answer: C. Diagnostic and
prognostic information
9. Enzymes are used in diagnostic kits for the
determination of various substances. The urease diagnostic kit is used for the
determination of which serum (plasma) component?
A. Glucose
B. Uric acid
C. Urea
D. Cholesterol
Correct Answer: C. Urea
10. In ELISA techniques, what are enzyme labels used
as a substitute for?
A. Hormones
B. Antibodies
C. Radioactive
isotopes
D. Drugs
Correct Answer: C. Radioactive isotopes
11. Enzymes are classified as special chemical
catalysts of what origin?
A. Synthetic
origin
B. Geological
origin
C. Biological
origin
D. Inorganic
origin
Correct Answer: C. Biological origin
12. Over 700 enzymes have been isolated in which form?
A. Gel form
B. Crystalline
or pure form
C. Liquid
suspension
D. Gaseous form
Correct Answer: B. Crystalline or pure form
13. How does a chemical catalyst behave during the
catalytic process?
A. It is
permanently altered.
B. It is
consumed.
C. It remains
unaltered and is not consumed.
D. Its mass is
greater than the products formed.
Correct Answer: C. It remains unaltered and
is not consumed.
14. What is the typical range of molecular weights for
some relatively small enzyme molecules?
A. In the order
of 10,000
B. In the order
of 150,000
C. Over a
million
D. Less than
1,000
Correct Answer: A. In the order of 10,000
15. Many enzymes exhibit absolute optical specificity
for at least a portion of what?
A. The end
product molecule
B. A substrate
molecule
C. A
competitive inhibitor
D. An inorganic
catalyst
Correct Answer: B. A substrate molecule
16. Which enzyme group acts specifically on
glycosides?
A. Esterases
B. Glycosidases
C. Pepsin
D. Trypsin
Correct Answer: B. Glycosidases
17. Which enzymes split off amino acids one at a time
from the amino-terminal end of polypeptide chains?
A.
Carboxylpeptidases
B. Chymotrypsin
C.
Aminopeptidases
D. Esterases
Correct Answer: C. Aminopeptidases
18. If only one substrate (S) is used, an
enzyme-catalyzed reaction is expressed as S 
. In the absence of enzyme (E), what happens?
A. The reaction
proceeds faster.
B. Very little
or no product (P) is formed.
C. The product
is immediately formed.
D. The reaction
becomes irreversible.
Correct Answer: B.
19. A chemical reaction involving the transformation
of 'S' into a product 'P' can proceed spontaneously only if there is a decrease
in what, in the course of the reaction?
A. Activation
energy
B. Substrate
concentration
C. Temperature
D. Free energy
or chemical potential
Correct Answer: D.
20. When S must first be converted to the transition
state (S*), what happens to the activation energy of the reaction?
A. It is
increased significantly.
B. It is
decreased.
C. It remains
unchanged.
D. It requires
high temperature.
Correct Answer: B. It is decreased.
21. In a non-catalytic chemical reaction, energy of
activation is typically provided in the form of what?
A. Low pH
B. High
temperature
C. Enzyme
concentration
D. Aqueous
solution
Correct Answer: B. High temperature
22. Enzymes tend to denature above what approximate
temperature?
A. 100 ˚C
B. 40 ˚C
C. 10 ˚C
D. 70 ˚C
Correct Answer: B. 40 ˚C
23. Compared to inorganic catalysts, how are enzymes
generally described regarding pH changes?
A. Not
sensitive to pH changes.
B. Sensitive to
pH changes.
C. Highly
active outside the pH 5.0-9.0 range.
D. Only
sensitive to metallic activators.
Correct Answer: B. Sensitive to pH changes.
24. Most of the enzyme-catalyzed reactions take place
in which type of solution?
A. Organic
solvent solutions
B. Acidic
solutions
C. Aqueous
solutions
D. Highly
concentrated solutions
Correct Answer: C. Aqueous solutions
25. The active site of an enzyme is perfectly
complementary to which state of the substrate?
A. The
original ground state
B. The product
state
C. The
transition state
D. The
intermediate complex
Correct Answer: C. The transition state
26. What is the defined small region at which the
substrate binds and participates in the catalysis?
A. The
allosteric site
B. The
catalytic groove
C. The active
site
D. The terminal
end
Correct Answer: C. The active site
27. The formation of the active site is primarily due
to the specific structure of the protein at which level?
A. Primary
structure
B. Secondary
structure
C. Tertiary
structure
D. Quaternary
structure
Correct Answer: C. Tertiary structure
28. Which of the following is listed as a factor that
affects enzyme activity?
A. Atmospheric
pressure
B. Ionic
strength
C. Density of
solution
D. Presence of
non-protein substrates
Correct Answer: B. Ionic strength
29. What term is used for the substrate concentration
that produces half maximum velocity (V_max)?
A. Optimum
velocity
B. Activation
constant
C. K_m value or
Michaelis constant
D. Isoelectric
point
Correct Answer: C. K_m value or Michaelis
constant,
30. When a reaction is said to be a zero order
reaction, what is true regarding the velocity (V) at high substrate
concentration (S)?
A. Velocity is
directly proportional to [S].
B. Velocity is
independent of the substrate concentration.
C. Velocity is
zero.
D. Velocity is
Vmax/2
Correct Answer: B. Velocity is independent
of the substrate concentration.
31. If an excess of substrate is present, what
typically happens to the rate of formation of end products if the enzyme
concentration is doubled?
A. Usually
halves the rate
B. Usually
doubles the rate
C. Has no
effect
D. Converts the
reaction to first order
Correct Answer: B. Usually doubles the rate
32. For animal enzymes, the optimal temperature for
the reaction typically approximates what temperature?
A. 0 ˚C
B. 100 ˚C
C. 37 ˚C
D. 50 ˚C
Correct Answer: C. Body temperature 37 ˚C
33. Over a limited range of values, the velocity of
many biological reactions roughly doubles with what temperature change?
A. A 5^\circ
\text{C} rise
B. A 10^\circ
\text{C} rise
C. A 20^\circ
\text{C} drop
D. A 37^\circ
\text{C} rise
Correct Answer: B. A 10^\circ \text{C} rise
34. Due to their protein nature, enzymes are very
sensitive to the concentration of what in their aqueous solutions?
A. Metallic
activators
B. Hydrogen ion
concentration (pH)
C. Substrate
concentration
D. Oxygen
concentration
Correct Answer: B. Hydrogen ion
concentration (pH)
35. Maximum enzyme activity is usually observed at or
near what point?
A. Denaturation
point
B. Freezing
point
C. Isoelectric
point
D. Titration
point
Correct Answer: C. Isoelectric point
36. Optimum activity is generally observed between
which pH values for most enzymes?
A. 1.0 and 4.0
B. 5.0 and 9.0
C. 10.0 and
14.0
D. 0.0 and 1.0
Correct Answer: B. 5.0 and 9.0
37. What is the optimum pH for the enzyme pepsin?
A. Between 7.0
and 8.0
B. Between 1.5
and 3.0
C. At 7.45
D. At 10.3
Correct Answer: B. Between 1.5 and 3.0
38. The activity of an enzyme drops quite rapidly to
zero if the pH is raised or lowered by more than how many units from the
optimum pH?
A. About 0.1 pH
units
B. About 1 pH
unit
C. About 2 pH
units
D. About 5 pH
units
Correct Answer: C. About 2 pH units
39. Oxidation of the sulfhydryl (-SH) groups in many
oxidoreductases results in the formation of what linkage, leading to loss of
enzyme activity?
A. Peptide
linkage
B. Hydrogen
linkage
C. Disulfide
(S-S) linkage
D. Ester
linkage
Correct Answer: C. Disulfide (S-S) linkage
40. When plotting Initial velocity (Vi) versus
substrate concentration [S], the maximum value reached is termed what?
A. Km
B. Vmax
C. Keq
D. S*
Correct Answer: B. Vmax
41. According to the Michaelis-Menten equation, when
the substrate concentration [S]is equal to the K-m value, what is the initial
velocity V-i?
A. Maximum
velocity Vmax
B. Half-maximum
velocity Vmax/2
C. Zero
D. Double the
maximum velocity
Correct Answer: B. Half-maximum velocity Vmax/2
42. The initial rate of an enzyme-catalyzed reaction
is always proportional to what?
A. The
concentration of the end product
B. The
concentration of the enzyme
C. The K_m value
D. The
incubation time
Correct Answer: B. The concentration of the
enzyme
43. Which type of method for enzyme determination is
preferred in clinical diagnosis due to being rapid and precise?
A. End point
reaction methods
B. Rate of
reaction methods
C. Gravimetric
methods
D. Colorimetric
methods using DNPH
Correct Answer: B. Rate of reaction methods
44. What name is given to the linear plot resulting
from inverting and factoring the Michaelis-Menten expression?
A. Arrhenius
Plot
B.
Lineweaver-Burk Plot
C.
Henderson-Hasselbalch Plot
D. Standard
Curve
Correct Answer: B. Lineweaver-Burk Plot,
45. How can the K_m value be estimated from a
Lineweaver-Burk plot?
A. From the
positive Y-intercept only
B. From the
slope, Y-intercept, or negative X-intercept
C. From the
slope only
D. By measuring
V_{max}
Correct Answer: B.
46. What is defined as a substance that binds with an
enzyme and causes a decrease in catalytic activity?
A. Substrate
B. Coenzyme
C. Enzyme
inhibitor
D. Positive
modifier
Correct Answer: C. Enzyme inhibitor
47. What type of inhibition involves the inhibitor
binding non-covalently with the enzyme, and can be reversed if the inhibitor is
removed?
A. Irreversible
inhibition
B. Allosteric
inhibition
C. Reversible
inhibition
D. Feedback
inhibition
Correct Answer: C. Reversible inhibition
48. In competitive inhibition, the inhibitor (I)
structurally resembles which molecule?
A. The product
B. The enzyme
C. The
substrate
D. A coenzyme
Correct Answer: C. The substrate
49. How can competitive inhibition be overcome?
A. By lowering
the temperature
B. By high
substrate concentration
C. By adding
heavy metals
D. By lowering
the pH
Correct Answer: B. By high substrate
concentration
50. Malonic acid, glutaric acid, and oxalic acid are
competitive inhibitors of which enzyme?
A. Amylase
B. Lactate
dehydrogenase (LDH)
C. Succinate
dehydrogenase (SDH)
D. Alkaline
phosphatase (ALP)
Correct Answer: C. Succinate dehydrogenase
(SDH)
51. What effect does competitive inhibition have on
the Michaelis constant (K_m) value?
A. K_m
decreases
B. K_m
increases
C. K_m remains
unchanged
D. K_m becomes
zero
Correct Answer: B. K_m increases
52. In noncompetitive inhibition, what is the effect
on the V_{max} value?
A. V_{max}
increases
B. V_{max} is
lowered
C. V_{max}
remains unchanged
D. V_{max}
becomes independent of enzyme concentration
Correct Answer: B. V_{max} is lowered
53. What is a characteristic of irreversible inhibition?
A. It can be
overcome by high substrate concentration.
B. The
inhibitors bind covalently with the enzymes.
C. The
inhibition is reversed by removing the inhibitor.
D. It affects
only V_{max}.
Correct Answer: B. The inhibitors bind
covalently with the enzymes.
54. Diisopropyl fluorophosphate (DFP) irreversibly
binds with enzymes containing which amino acid, such as serine proteases?
A. Cysteine
B. Glutamate
C. Serine
D. Arginine
Correct Answer: C. Serine
55. Some enzymes possess additional sites, besides the
active site, known as what?
A. Transition
sites
B. Allosteric
sites
C. Substrate
sites
D. Peptide
sites
Correct Answer: B. Allosteric sites
56. What are allosteric modulators that increase
enzyme activity called?
A. Negative
allosteric modulators
B. Irreversible
modulators
C. Competitive
inhibitors
D. Positive
allosteric modifiers
Correct Answer: D. Positive allosteric modifiers
57. Which class of molecules frequently acts as
inorganic positive modifiers for enzymes?
A. Metal ions
B. Fatty acids
C.
Carbohydrates
D. Nucleic
acids
Correct Answer: A. Metal ions
58. Which metallic ion is required for all phosphate
transfer reactions?
A. Iron (Fe)
B. Molybdenum
(Mo)
C. Copper (Cu)
D. Magnesium
(Mg)
Correct Answer: D. Magnesium (Mg)
59. What may act as inorganic negative modifiers by
converting an active configuration of an enzyme into an inactive form?
A. Heavy metal
ions (e.g., lead, silver, gold)
B. Magnesium
ions
C. Coenzymes
D. B-complex
vitamins
Correct Answer: A. Heavy metal ions (e.g.,
lead, silver, gold),
60. What is the nonprotein organic compound required
by many enzymes to catalyze reactions of their substrates?
A. Positive
modifier
B. Coenzyme
C. Heavy metal
D. Tertiary
structure
Correct Answer: B. Coenzyme
61. What is the term for the complete system
containing both the enzyme (protein) and the required coenzyme (dialyzable,
nonprotein organic substance)?
A. Apoenzyme
B. Holoenzyme
C. Zymogen
D. Isoenzyme
Correct Answer: B. Holoenzyme
62. Lytic reactions, including hydrolytic reactions,
are generally characterized by not requiring what?
A. Water
B. Substrate
C. Coenzymes
D. A protein
structure
Correct Answer: C. Coenzymes
63. Coenzymes frequently contain which nutritional
component as part of their structure?
A. Vitamin C
B. B-complex
vitamins
C. Vitamin A
D. Vitamin D
Correct Answer: B. B-complex vitamins
64. NAD+ and NADP+ are listed as coenzymes primarily
for the transfer of which atom or group?
A. Phosphate
group (P)
B. Methyl group
(CH_3)
C. Hydrogen (H)
D. Carbon
dioxide (CO_2)
Correct Answer: C. Hydrogen (H)
65. What are physically distinct forms of the same
enzyme, having the same catalytic activity, called?
A. Coenzymes
B. Allosteric
modifiers
C. Holoenzymes
D. Isoenzymes
Correct Answer: D. Isoenzymes
66. Isoenzymes may differ in which property?
A. Identical
catalytic activity
B. Stability to
heat denaturation
C. Identical
primary structure
D. Identical
molecular weights
Correct Answer: B. Stability to heat
denaturation
67. Which lactate dehydrogenase isoenzyme is richest
in cardiac muscle and moves fastest towards the anode in electrophoresis?
A. LD_5
B. LD_1
C. LD_3
D. LD_4
Correct Answer: B. LD_1
68. The heart isoenzyme of creatine phosphokinase (CK)
is composed of which two units?
A. BB type
B. MM type
C. MB type
D. AA type
Correct Answer: C. MB type
69. Under the IUB classification system, the suffix
added to the substrate name or reaction type to designate the enzyme is what?
A. -zyme
B. -oid
C. -ase
D. -in
Correct Answer: C. -ase,
70. Which IUB enzyme class catalyzes oxidation and
reduction reactions between two substrates?
A. Transferases
B. Lyases
C.
Oxidoreductases
D. Hydrolases
Correct Answer: C. Oxidoreductases
71. Enzymes that catalyze the transfer of a group G
(other than hydrogen) between a pair of substrates are classified as which IUB
class?
A.
Oxidoreductases
B. Transferases
C. Hydrolases
D. Isomerases
Correct Answer: B. Transferases
72. Lyases are enzymes that catalyze the removal of
groups from substrates by a mechanism other than hydrolysis, leaving what?
A. Single bonds
B. Double bonds
C. Peptide
bonds
D. Ester bonds
Correct Answer: B. Double bonds
73. The enzyme classification group Isomerases
catalyzes the interconversion of what?
A. Substrates
and coenzymes
B. Metal ions
C. Optical,
geometric, or positional isomers
D. ATP and ADP
Correct Answer: C. Optical, geometric, or
positional isomers
74. Ligases are enzymes that link together two
compounds, coupled to the breaking of what type of bond in a compound such as
ATP?
A.
Phosphodiester bond
B. Peptide bond
C.
Pyrophosphate bond
D. Glycosyl
bond
Correct Answer: C. Pyrophosphate bond
75. Enzymes like lipoprotein lipase and
pseudocholinesterase, whose substrates are present in circulation and perform a
physiologic function in blood, are grouped as what type of plasma enzyme?
A.
Nonfunctional enzymes
B.
Intracellular enzymes
C. Functional
enzymes (plasma active)
D. Exocrine
secretion enzymes
Correct Answer: C. Functional enzymes
(plasma active)
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