BIOCHEM Ch. 12
II, IV
A Lineweaver-Burk plot is also referred to as I. a sigmoidal plot. II. a linear plot. III. a Michaelis-Menten plot. IV. a double reciprocal plot.
phosphorylation
A common type of covalent modification of regulatory enzymes involves ______ of serine residues.
a competitive inhibitor
A compound that distorts the active site, rendering the enzyme catalytically inactive is called
Yes
A lab recently developed a new drug which is hypothesized to inhibit the enzyme cyclooxygenase-2 (COX-2) and reduce inflammation. In their first test they monitored the reaction of substrate as it is converted to product in the presence of the new drug (data shown below). If the hypothesis is correct the observed initial rate will be at least 2 times slower than the normal reaction without the drug. If the normal initial rate is 30 mM/s, does the data below indicate that the team has designed a successful inhibitor?
small KS
A lead compound for a new drug should bind to its target protein with a very ___
KI = 1.5X10^-8 M
A lead compound would be most promising if it had:
competitive inhibitor
A new drug has been discovered which inhibits the reaction catalyzed by enzyme A. Based on the information shown below, what is this drug?
the type of inhibition is competitive
A plot of 1/V vs. 1/[S] for an enzyme catalyzed reaction gave a line with an equation of y = 0.5x + 0.2. The same enzyme with an inhibitor present gave a line with an equation of y = 1.1x + 0.2. Which of the following statements is true?
Ping Pong
A two-substrate enzymatic reaction in which one product is produced before the second substrate binds to the enzyme has a ______ mechanism.
a chemically modified enzyme-intermediate
All are characteristics of ordered single-displacement reactions EXCEPT:
All are true
All are characteristics of ribozymes EXCEPT:
All are true
All are characteristics of the enzyme hexokinase EXCEPT:
ability to change deltaG
All are distinctive features of enzymes EXCEPT:
All are true
All are true for catalysts EXCEPT:
It binds a site other than the active site
All are true for inhibitor I if it is a competitive inhibitor EXCEPT:
all are true
All are true for kcat EXCEPT :
They are protein components
All of the following are properties of a coenzyme EXCEPT:
The energy required to raise the average energy of one mole of reactant to the transition state is the free energy of activation
All of the following are true statements about the transition state of a reaction EXCEPT:
In the presence of a competitive inhibitor, the apparent Km would be altered and Vmax would be decreased
All of the following statements about competitive inhibition are correct EXCEPT:
Increasing the concentration of [S] can overcome the inhibition
All of the following statements about noncompetitive inhibition are true EXCEPT:
Km = Vmax/2
All of the following statements are true about the relationships between [S], Km and Vmax EXCEPT:
stabilize conformations with higher substrate affinity
Allosteric activators
the velocity will be 20 mM/min
An enzymatic reaction has a Vmax of 30 μM/min and a Km of 50 μM. If the concentration of the substrate is 25 μM, which of the following is true?
kcat/KM is near 108 M-1s-1.
An enzyme is near maximum efficiency when
molecular recognition based on structural complementarity
An enzyme's specificity can be due to:
The reverse reaction (breakdown of EA to E+A) was favored, slowing the Vmax
An extremely efficient enzyme called "efficase" catalyzes the conversion of "A" to "B." A researcher decides to mutate the enzyme in order to try to improve its performance. Following active site mutations, a significant reduction in the value of KM and Vmax was observed. Which of the following may have occurred?
[A]
Assume a first order reaction, the rate of the reaction 2A→B is dependent on ______.
the rate of reaction is expected to be directly proportional to substrate concentration
At substrate concentrations much lower than the enzyme concentration,
B = KM
Based on the figure in the question above (question 54), which of the following expressions would correctly define KM?
D = 1/Vmax
Based on the figures below, which of the following expressions would be correct?
carbonic anhydrase binds CO2 well and converts it to carbonic acid very well
Carbonic anhydrase has two substrates, carbon dioxide and bicarbonate, which are both converted to carbonic acid. Kinetic data for each is given below. Typical values for Kcat/Km range from less than 1 mM-1sec-1 to as high as 2.8×105 mM-1sec-1. What can be said about the Kcat/Km for CO2?
CO2 would act as a competitive inhibitor
Carbonic anhydrase has two substrates, carbon dioxide and bicarbonate, which are both converted to carbonic acid. Kinetic data for each is given below. While determining the kinetics of HCO3- as a substrate, how would the addition of CO2 effect the reaction if the rate were measured by the disappearance of bicarbonate?
abzymes; an analog of the transition-state intermediate in the reaction
Catalytic antibodies, also called ____, are generated against an antigen that is:
I, II, III
Compounds that function as "mixed inhibitors" I. interfere with substrate binding to the enzyme. II. bind to the enzyme reversibly. III. can bind to the enzyme/substrate complex.
KM=[33]; Vmax=167/s
Determine the KM and Vmax from the following graph. (Note: On the x-axis the minor tick mark spacing is 0.005; on the y-axis the minor tick mark spacing is 0.002)
isozymes
Different enzymes that catalyze the same reaction, although may be found in different tissues, are known as ______.
sequential - Random
Enzyme E is responsible for conversion of substrate X to product U. As a result of this conversion electrons are transported to a coenzyme (FAD) within Enzyme E. In order for the reaction to be completed, a second substrate NAD+ must also bind Enzyme E and collect stored electrons (which converts it to product, NADH). The graph below shows the data while varying X, with fixed concentrations of NAD+. What type of multi-substrate mechanism does enzyme E utilize?
I, II, III, IV
Enzyme activity in cells is controlled by which of the following? I. covalent modifications II. modulation of expression levels III. feedback inhibition IV. allosteric effectors
lowering the activation energy of the reaction
Enzymes work by:
8X10^7 min-1
Find kcat for a reaction in which Vmax is 4 × 10-4 mol•min-1 and the reaction mixture contains one microgram of enzyme (the molecular weight of the enzyme is 200,000 D).
2.6X10^-5 molsec-1
Find the initial velocity for an enzymatic reaction when Vmax = 6.5 × 10-5 mol•sec-1, [S] = 3.0 × 10-3 M, KM = 4.5 × 10-3 M and the enzyme concentration at time zero is 1.5 × 10-2 μM.
This data may have been collected both in the absence (solid line) and presence (dashed line) of a mixed (noncompetitive) inhibitor.
Following several experiments, the data presented on the graph below was obtained. What can you determine from this graph?
pseudo-first-order
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
0.60 mM
For an enzyme-catalyzed reaction, the initial velocity was determined at two different concentrations of the substrate. Which of the following would be closest to the value of Km?
3.19 mM/min
For an enzyme-catalyzed reaction, the initial velocity was determined at two different concentrations of the substrate. Which of the following would be closest to the value of Vmax?
ES breakdown occurs at the same rate as ES formation
For the reaction, the steady state assumption
none of the above
Fourth-order reactions.
18 mM
From the graph below plotting data that was collected under steady state conditions, velocity on the y-axis in units of μM/s and substrate concentration of the x-axis in units of μM, what is the KM?
0.24 mM/s
From the graph below plotting data that was collected under steady state conditions, velocity on the y-axis in units of μM/s and substrate concentration of the x-axis in units of μM, what is the Vmax?
They lower the energy of activation
How do catalysts work to accelerate a chemical reaction?
A competitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in Vmax
I propose to design a new drug which will act as an inhibitor for an enzyme. If I have used all current information about the mechanism of this enzyme to design this inhibitor and I carefully engineer it with similar chemical properties of the transition state, what type of inhibitor am I attempting to engineer and how will I know if I have succeeded?
mixed noncompetitively inhibited reaction
Identify the type of reaction that would give the following graph:
the rate constant
If A→B is a zero-order reaction, the rate is dependent on ______.
2.5 mM/min
If an enzyme has a Vmax of 15 mM/min, what is the velocity if the substrate is present at 1/5 of the Km?
10^11
If the rate constant for the enzyme catalyzed reaction is 2 × 105/sec and the rate constant for the uncatalyzed reaction is 2 × 10−6/sec, the catalytic power of the enzyme is:
competitive inhibition
In ______, the inhibitor binds to a site involved in both substrate binding and catalysis.
[S] would need to be 3KM
In order for an enzymatic reaction obeying the Michaelis-Menten equation to reach 3/4 of its maximum velocity,
No, the reaction is random single-displacement
In the enzyme catalyzed reaction sequence below, can the E-PO4− intermediate be predicted and why?
E-pyridoxal phosphate complex
In the glutamate:aspartate aminotransferase catalyzed reaction mechanism, glutamate would react with ____ to form α-ketoglutarate
Yes, it is 30 mM
In the plot below, can the KM be determined? If so, what is its value?
P and A
In the reaction mechanism below, ____ are competitive for binding to free enzyme E
x-intercept is 1/Km
In transforming the Michaelis-Menten equation into a straight line equation, y = mx + b, the Lineweaver-Burk double reciprocal plot, which of the following is NOT a true representation?
ES complex
In uncompetitive inhibition, the inhibitor binds only to the ______.
I combines only with ES
In uncompetitive inhibition:
inactivate the enzyme
Irreversible enzyme inhibitors
is the concentration of substrate where the enzyme achieves ½ Vmax
KM
the [S] that half-saturates the enzyme
KM is
competitive inhibition
Malonate inhibition of succinate dehydrogenase is an example of:
I or II, III
Parallel lines on a Lineweaver-Burk plot indicate I. an increase in KM. II. decrease in KM. III. decrease in Vmax. IV. uncompetitive inhibition.
amide
Penicillin and other β-lactam antibiotics form a covalent bond to the enzyme glycoprotein transpeptidase. What type of bond is formed?
suicide substrate
Penicillin is an example of a mechanism-based enzyme inactivator and is a(n):
the phosphorylation of a wide variety of proteins
Protein kinases are involved in
none of the above
Pseudo-first-order reaction kinetics would be observed for the reaction A + B -> C
is dependent on the concentration of A and B
Reaction that is first order with respect to A and B
cGMP phosphodiesterases
Sildenafil citrate (Viagra) was developed as an inhibitor of:
bimolecular
The E+S -> E+P reaction is ______.
micromoles of product formed per minute
The International Units of an enzyme are based on the:
k2<<k-1
The KM can be considered to be the same as the dissociation constant KS for E + S binding if
I
The Michaelis constant KM is defined as I. (k-1 + k2)/k1 II. ½ Vmax III. [S] = [ES] IV. [ES]/2
0.014 M
The breakdown of dopamine is catalyzed by the enzyme monoamine oxidase (MAO). What is the final concentration of product if the starting dopamine concentration is 0.050 M and the reaction runs for 5 seconds. (Assume the rate constant for the reaction is 0.249 s−1.)
k1
The catalytic efficiency of an enzyme can never exceed
holoenzyme
The catalytically active complex of an apoenzyme and its prosthetic group is referred to a(n) ____.
The Vmax equals 200 M/s
The following data were collected under conditions indicated in the graph below during the time period of 0-5 seconds. Upon plotting the Lineweaver-Burk plot, the information given in the table below was determined. Based on this available information which of the following is FALSE?
The energy required to raise the average energy of one mole of reactant to the transition state energy
The free energy of activation, ΔG, is defined as:
both C and D are correct
The pH optimum of an enzyme is:
substrate; active
The specific site on the enzyme where ____ binds and catalysis occurs is called the ____ site.
isomerase
The trivial term for an enzyme that moves a functional group from one place to another on the substrate is ___________,
competitive inhibition
The type of enzyme inhibition in which Vmax is unaffected is ______.
random bisubstrate reaction
This diagram refers to a (an)
4.8 × 102 Msec-1
What is the velocity of a first-order reaction at 37oC when the reactant concentration is 6 × 10-2 M and the rate constant is 8 × 103 sec-1?
A reaction with a rate constant in the units of s−1
What reaction would NOT proceed via bimolecular elementary steps?
0.5
When [S] = KM, ν0 = (_____)× (Vmax).
zero; Vmax
When every enzyme molecule in the reaction mixture has its substrate-binding site occupied by substrate, the kinetics become ____-order, and the velocity is ____.
The reaction is zero order with respect to [S] if [S]>>[E]
Which of the following is (are) true?
X=B, Y=A, Z=Q
Which of the following is correct in regards to the diagram above?
The concentration of the enzyme-substrate complex reaches a constant value even in a dynamic system
Which of the following is true regarding the Briggs and Haldane steady state assumption?
It reflects the property of the enzyme when substrate concentration is at saturation.
Which of the following statements is NOT characteristic of kcat/Km?
metabolic pathways are necessary since enzymes usually catalyze only one specific reaction
Which of the following statements is true regarding enzyme pathways?
a competitive inhibitor results in a higher apparent Km value
Which of the following statements regarding inhibitors is correct?
It is numerically equal to the substrate concentration required to achieve one half the maximum velocity
Which statement is correct about the Michaelis-Menten constant, Km, for the kinetic mechanism below?
(1/3) Vmax
[S] = KM for a simple enzymatic reaction. When [S] is doubled the initial velocity is
Phase 2; single blind
________ clinical trials are focused on evaluating the efficacy of new drug candidates, and usually use _____ test.
