Download Chapter 11: Enzyme Catalysis

Chapter 11: Enzyme Catalysis
Matching
A)
B)
C)
D)
E)
F)
G)
H)
I)
J)
K)
L)
M)
N)
high
deprotonated
protonated
least resistance
motion
rate-determining
leaving group
short peptides
amino acid
low
coenzymes
concerted acid-base
orient
oxidoreductase
1. For efficient nucleophilic catalysis, a group such as the sulfhydryl on a cysteine residue must
be able to form a good ______, in addition to being a good nucleophile.
2. If an enzyme-catalyzed reaction has a low rate at low pH and high rate at higher pH, this
implies that a group on either the enzyme or the substrate must be ______ for an efficient
reaction.
3. On a transition state diagram for a multistep reaction, the step with the greatest G is the
______ step.
4. On a transition state diagram for a one-step, very spontaneous reaction (large negative G),
a large peak (high G°) would imply a ______ rate for the reaction.
5. Metal ion cofactors can ______ the substrate at the active site, providing catalytic
enhancement.
6.
Large rate enhancement in enzyme catalysis may occur when the binding of substrate
reduces the ______ of the reacting groups.
7. Metal ion cofactors with more than one oxidation state may assist in catalysis by the ______
class of enzymes.
8. Since proteins are limited in their abilities to catalyze oxidation-reduction reactions,
enzymes often employ ______ to assist with catalysis.
9. Some serine proteases are believed to have developed by convergent evolution, because the
______ sequences of some serine proteases show no resemblance to those of others.
10. Clustering several amino acid residues with favorable pK values at an active site can
promote a(n) _________ catalytic mechanism.
11.
A)
B)
C)
D)
E)
Which of these amino acid groups would not make a good nucleophilic catalyst?
amino
sulfhydryl
imidazole
methyl
hydroxyl
12. The imidazole side chain of histidine can function as either a general acid catalyst or a
general base catalyst because:
A) in the physiological pH range both H+ and OH– are present at high concentrations.
B) in the physiological pH range, the nitrogen in the ring can be easily
protonated/deprotonated.
C) one guanidino group is protonated, and the other is deprotonated at physiological pH.
D) the imidazole group is a strong reducing agent at physiological pH.
E) the sulfur atoms in the ring can either gain or lose a proton at physiological pH.
13. Chymotrypsin, a serine protease, preferentially cleaves a peptide bond adjoining a bulky
non-polar side chain. This is because chymotrypsin's specificity pocket:
A) contains a sulfhydryl group that forms a disulfide bond with the substrate.
B) is lined with small hydrophobic side chains, leaving considerable room in the nonpolar
pocket.
C) contains a negative charge.
D) is mostly filled with large side chains.
E) contains a positive charge.
14. Which one of the following is correct?
A) All enzymes are highly specific for the reactions they catalyze.
B) Prosthetic groups are loosely associated with the polypeptide chain of an enzyme.
C) Activation of zymogens, such as proelastase, requires an oxidation-reduction reaction at a
particular amino acid side chain.
D) If an enzyme-catalyzed reaction requires a group with a low pK to be deprotonated and a
group with a higher pK to be protonated, the pH vs. velocity curve will have a peak in the
middle.
E) The proximity effect, a result of bringing substrates close to their catalytic groups in the
active site, can result in a rate enhancement on the order of 106.
15. Which of the following amino acid residues would not provide a side chain for acid-base
catalysis?
A) leucine
B) serine
C) lysine
D) aspartic acid
E) histidine
17. _______ is a serine protease that has a specificity pocket that binds small hydrophobic side
chains.
A) chymotrypsin
B) trypsin
C) lysozyme
D) trypsinogen
E) elastase
18.
as:
A)
B)
C)
D)
E)
Simultaneous stimulation of a reaction by general acid and general base catalysis is defined
covalent catalysis.
electrostatic catalysis.
proximity catalysis.
concerted acid/base catalysis.
transition-state catalysis.
19. The formation of a Schiff base in the enzymatically catalyzed decarboxylation of
acetoacetate is an example of:
A) covalent catalysis.
B) electrostatic catalysis.
C) proximity catalysis.
D) concerted acid/base catalysis.
E) transition-state catalysis.
20. The ‘catalytic triad’ in chymotrypsin consists of:
A)
B)
C)
D)
E)
substrate, transition state, and product
enzyme, substrate, and metal-ion cofactor
three amino acids: SER, HIS, and ASP
three amino acids: CYS, HIS, and ASP
three amino acids: SER, HIS, and GLU
Chap 12
1. What is the velocity of a first-order reaction when the reactant concentration is 6 x 10-2 M
and the rate constant is 8 x 103 sec-1?
A) 1.33 x 105 M-1•sec-1
B) 1.33 x 105 M•sec
C) 7.5 x 10-2 M•sec
D) 4.8 x 102 M•sec-1
E) not enough data are given to make this calculation
2. For a reaction A + B  C, if the concentration of B is much larger than [A] so that [B]
remains constant during the reaction while [A] is varied, the kinetics will be:
A) sigmoidal
B) pseudo-first-order
C) unimolecular
D) zero-order
E) enzymatic
3.
A)
B)
C)
D)
E)
KM is:
a measure of the catalytic efficiency of the enzyme.
the rate at which the enzyme dissociates from the substrate.
the rate constant for the reaction ES  E + P.
the [S] that half-saturates the enzyme.
the rate at which the enzyme binds the substrate.
4.
A)
B)
C)
D)
E)
The KM can be considered to be the same as the dissociation constant KS for E + S binding if:
this statement cannot be completed because KM can never approximate KS.
ES  E + P is fast compared to ES  E + S.
the turnover number is very large.
k2 << k-1.
kcat/KM is near the diffusion-controlled limit.
5.
A)
B)
C)
An enzyme is considered to have evolved to its most efficient form if
kcat is a large number
kcat/KM is near the diffusion-controlled limit
KM is a large number
D) kcat/KM is a very small number
E) KM is a small number
6. Find the initial velocity for an enzymatic reaction when Vmax = 6.5 x 10–5 mol•sec–1, [S] =
3.0 x 10–3 M, and KM = 4.5 x 10–3 M.
A) not enough information is given to make this calculation
B) 2.6 x 10–5 mol•sec–1
C) 1.4 x 10–2 mol•sec–1
D) 8.7 x 10–3 mol•sec–1
E) 3.9 x 10–5 mol•sec–1
7.
A)
B)
C)
D)
E)
Parallel lines on a Lineweaver-Burk plot are diagnostic of:
competitive inhibition.
non-competitive inhibition.
allosteric activation.
allosteric inhibition.
none of the above.
The following questions refer to the overall transformation:
8.
A)
B)
C)
D)
E)
The overall transformation
is composed of two elementary reactions.
can be zeroth order in [S] if [S]>>[E]
may be described by the Michaelis-Menten equation if certain assumptions are made
all of the above
none of the above
9.
A)
B)
C)
D)
E)
For the reaction, the steady state assumption assumes that
[S] = [P]
[ES] is constant
[P]>>[E]
[P] is constant
k–1>>k2
10. The Michaelis constant KM is defined as
A) (k–1 + k2)/k1
B) (k–1 + k1)/k2
C) ([P] + [E])/[ES]
D) [ES]
E) none of the above
11.
The most efficient enzymes have kcat/KM values that approach
A)
B)
C)
D)
E)
k2
k1
k–1
k–1 + k2
1012 M•s–1
12. A compound that reduces the concentration of enzyme available for substrate binding is
called:
A) a transition-state analog
B) a non-competitive inhibitor
C) an allosteric effector
D) an enzyme inactivator
E) a competitive inhibitor
13.
A)
B)
C)
D)
E)
Compounds that function as ‘mixed inhibitors’
interfere with substrate binding to the enzyme
bind to the enzyme reversibly
can bind to the enzyme/substrate complex
all of the above
none of the above
14.
A)
B)
C)
D)
E)
Enzyme activity in cells is controlled by processes including:
temporary covalent modifications.
modulation of expression levels.
feedback inhibition.
binding to allosteric effectors.
all of the above.
15.
A)
B)
C)
D)
E)
Allosteric activators bind to enzymes
in a way to inhibit substrate binding.
and stabilize the ‘T-state’, which has a low substrate affinity.
and stabilize the ‘R-state’, which has an enhanced substrate affinity.
covalently.
none of the above.
16.
A)
B)
C)
D)
E)
Protein kinases are involved in
the digestion of drugs to potentially toxic byproducts
the degradation of enzymes to the component amino acids
the phosphorylation of a wide variety of proteins
the metabolism of drugs to water-soluble, excretable compounds
all of the above
Chapter 13: Biochemical Signaling
1. Insulin binds to a receptor that
A)
B)
C)
D)
E)
is coupled to a G protein.
possesses tyrosine kinase activity.
possesses serine/threonine phosphatase activity.
migrates to the nucleus to affect transcription.
activates MAP kinase.
2. The ability of receptors to adapt to long-term stimulation by responding to changes in
stimulation rather than the level of stimulation is called
A)
B)
C)
D)
E)
dual-specificity
signal transduction
autoinhibition
desensitization
an emergent property
3. The interaction of various signaling pathways is called
A)
B)
C)
D)
E)
dual-specificity
signal transduction
autoinhibition
desensitization
cross-talk
4. Phospholipase C cleaves PIP2, generating
A)
B)
C)
D)
E)
IP3 and DAG (inositol-1,4,5-trisphosphate and 1,2-diacylglycerol)
cAMP and PPi
cAMP and DAG
IP3 and PPi
IP3 and Pi
5. G proteins
A)
B)
C)
D)
E)
consist of three subunits, G, G, and G
hydrolyze GTP to GMP + Pi + Pi
completely span the cell membrane
A and B
A and C
6. The insulin signaling pathway includes the following steps:
A)
B)
ligand-induced dimerization of the receptor and phosphorylation of IRS-1 and/or
IRS-2 proteins
autophosphorylation and phosphorylation of IRS-1 and/or IRS-2 proteins
C)
D)
E)
IRS-1–induced dimerization of the receptor, autophosphorylation, and
phosphorylation of SH2 domains
autophosphorylation and dephosphorylation of IRS-1 and/or SH2 domains
none of the above
7. What is (are) the advantages of protein phosphorylation as a signaling event?
A)
B)
C)
D)
E)
Phosphorylation is rapid and specific.
Phosphorylation is enzymatically reversible.
Phosphorylation can be amplified by cascade systems.
A and B
A, B, and C
8. Which of the following is a secondary messenger?
A)
B)
C)
D)
E)
insulin
epinephrine
cortisol
cyclic AMP
rhodopsin
9. Ras is an example of
A)
B)
C)
D)
E)
a monomeric G protein
a heterotrimeric G protein
a receptor protein
a cytokine
an interferon
10. Which of the following is (are) associated with cAMP binding to cAMP-dependent protein
kinase A?
A)
B)
C)
D)
E)
cAMP binds to the regulatory subunits
regulatory subunits dissociate from catalytic subunits
catalytic subunits phosphorylate multiple targets with specifc serines and threonines
A and B
A, B, and C
11. Which of the following statements concerning the action of G proteins on adenylate cyclase
is true?
A)
B)
C)
D)
G proteins always serve to activate adenylate cyclase.
G proteins always serve to inhibit adenylate cyclase.
Some G proteins activate adenylate cyclase, while others inhibit it.
G proteins do not act on adenylate cyclase at all.