BIOCHEMISTRY EXAM 3 REVISION
QUESTIONS AND THEIR ANSWERS
Which of the following statements about enzymes are
true:
1. Catalysis occurs at the active site, which usually
consists of a crevice on the surface of the enzyme.
2. Generally, an enzyme is specific for a particular
substrate. For example, thrombin catalyzes the
hydrolysis of the peptide bond between Arg and Gly.
3. An enzyme yields a specific product, whereas a
nonbiological catalyst may produce more than one
product, and side reactions may occur.
4. Nonbiological catalysts and enzymes tend to have a
similar degree of reaction specificity.
5. A substrate must bind to the active site before
catalysis can occur.
1,2,3,5
general enzyme-catalyzed reaction.
E + S ↔ ES ↔ E + P
What effects are produced by an enzyme on the
general reaction below
S↔P
k1→
k2←
2. the activation energy for the reaction is lowered.
,3. the rate constant for the reverse reaction (k2)
increases.
4. ∆G for the reaction decreases.
5. The formation of the transition state is promoted.
6.The concentration of the products is increased.
2,3,5
Which of the following interactions can contribute to
the intrinsic binding energy during enzymatic
catalysis:
1. permanent covalent bonding
2. electrostatic interactions
3. nucleophilic attack by serine
4. hydrogen bonding
5. van der waals interactions
2, 4, 5
sort the following into: acid-base catalysis, covalent
catalysis, metal ion catalysis, or all.
1. catalyst retains its original form after reaction
occurs.
2. a proton is transferred between enzyme and
substrate.
3. a covalent bond forms between enzyme and
substrate.
4. may use amino acids such as aspartate or lysine for
protonation or proton abstraction.
5. may take part in interactions involving Fe2+.
6. Catalysts may participate in oxidation-reduction
reactions by changes in the oxidation state.
7. uses a nucleophilic function group.
, 8. lowers the energy or stabilizes the transition state
or intermediate.
9. a Zn2+ cofactor may properly orient the substrate in
the active site through ionic interactions.
10. two-part catalytic process(for example, the
chymotrypsin mechanism).
acid-base catalysis: 2, 4
covalent catalysis: 3, 7, 10
metal ion catalysis: 5,6,9
all: 8, 1
suppose that an arginine residue in the active site of
an enzyme was mutated to alanine. as expected, the
alanine mutant was inactive, suggesting that the
arginine residue was critical to the catalytic
mechanism.
which mutantion is most likely to restore wild-type
level of activity to the alanine mutant.
a to e
a to k
a to m
a to y
a to s
A TO K
sort the following into lock-and-key model, induced-fit
model, or common to both.
1. substrate binds to the enyzme at the active site,
QUESTIONS AND THEIR ANSWERS
Which of the following statements about enzymes are
true:
1. Catalysis occurs at the active site, which usually
consists of a crevice on the surface of the enzyme.
2. Generally, an enzyme is specific for a particular
substrate. For example, thrombin catalyzes the
hydrolysis of the peptide bond between Arg and Gly.
3. An enzyme yields a specific product, whereas a
nonbiological catalyst may produce more than one
product, and side reactions may occur.
4. Nonbiological catalysts and enzymes tend to have a
similar degree of reaction specificity.
5. A substrate must bind to the active site before
catalysis can occur.
1,2,3,5
general enzyme-catalyzed reaction.
E + S ↔ ES ↔ E + P
What effects are produced by an enzyme on the
general reaction below
S↔P
k1→
k2←
2. the activation energy for the reaction is lowered.
,3. the rate constant for the reverse reaction (k2)
increases.
4. ∆G for the reaction decreases.
5. The formation of the transition state is promoted.
6.The concentration of the products is increased.
2,3,5
Which of the following interactions can contribute to
the intrinsic binding energy during enzymatic
catalysis:
1. permanent covalent bonding
2. electrostatic interactions
3. nucleophilic attack by serine
4. hydrogen bonding
5. van der waals interactions
2, 4, 5
sort the following into: acid-base catalysis, covalent
catalysis, metal ion catalysis, or all.
1. catalyst retains its original form after reaction
occurs.
2. a proton is transferred between enzyme and
substrate.
3. a covalent bond forms between enzyme and
substrate.
4. may use amino acids such as aspartate or lysine for
protonation or proton abstraction.
5. may take part in interactions involving Fe2+.
6. Catalysts may participate in oxidation-reduction
reactions by changes in the oxidation state.
7. uses a nucleophilic function group.
, 8. lowers the energy or stabilizes the transition state
or intermediate.
9. a Zn2+ cofactor may properly orient the substrate in
the active site through ionic interactions.
10. two-part catalytic process(for example, the
chymotrypsin mechanism).
acid-base catalysis: 2, 4
covalent catalysis: 3, 7, 10
metal ion catalysis: 5,6,9
all: 8, 1
suppose that an arginine residue in the active site of
an enzyme was mutated to alanine. as expected, the
alanine mutant was inactive, suggesting that the
arginine residue was critical to the catalytic
mechanism.
which mutantion is most likely to restore wild-type
level of activity to the alanine mutant.
a to e
a to k
a to m
a to y
a to s
A TO K
sort the following into lock-and-key model, induced-fit
model, or common to both.
1. substrate binds to the enyzme at the active site,
