Biochem Exam 2 Questions
If an enzyme-catalyzed reaction has a velocity of 2 mM/min and a Vmax of 10 mM/min when the substrate concentration is 0.5 mM, what is the KM? A) 0.2 mM B) 0.5 mM C) 1 mM D) 2 mM E) 5 mM
D) 2mM
If a Lineweaver-Burk plot gave a line with an equation of y = 0.490 x + 0.059, what is the velocity at a substrate concentration of 5 mM? The original units for substrate were in mM and velocity in mM/s. A) 0.288 mM/s B) 0.399 mM/s C) 2.51 mM/s D) 6.37 mM/s E) the velocity cannot be determined from this data
D) 6.37 mM/s
Which of the following is the most effective way to increase the rate of a biochemical reaction? A) increase the temperature B) increase the concentrations of the reactants C) increase or decrease the pH D) add a catalyst E) none of the above
D) Add a catalyst
The ability for an enzyme to change its shape upon substrate binding represents the concept of _________________.
Induced fit
What amino acid residue present in the specificity pocket allows trypsin to bind peptides containing the basic residues, Arg or Lys?
Asp
What are the three main amino acids found in the catalytic triad of chymotrypsin?
Asp, His, Ser
What percentage of Vmax is obtained when the substrate is present at ¼ of the KM? ` A) 5% B) 20% C) 25% D) 80% E) 100%
B) 20%
If the Asp in the chymotrypsin active site was mutated to another amino acid, which of the following would be considered an invisible mutation in that it is least likely to impact the function of the enzyme? A) Asp --> Asn B) Asp --> Glu C) Asp --> His D) Asp --> Ser E) Asp --> Lys
B) Asp --> Glu
Which of the following types of inhibition can be reversed by addition of more substrate? A) noncompetitive inhibition B) competitive inhibition C) uncompetitive inhibition D) irreversible inhibition E) none of the above
B) Competitive inhibition
An enzyme that forms a covalent bond with its substrate during the course of a reaction is considered to undergo _____. A) acid-base catalysis B) covalent catalysis C) electrophilic catalysis D) metal ion catalysis E) none of the above
B) Covalent catalysis
A plot of velocity versus substrate concentration for a simple enzyme-catalyzed reaction produces a _____. This indicates that at some point, the enzyme is _____. A) straight line; inhibited by product B) hyperbolic curve; saturated with substrate C) sigmoidal curve; inhibited by substrate D) hyperbolic curve; activated by substrate E) sigmoidal curve; saturated with substrate
B) Hyperbolic curve; saturated with substrate
The ability for an enzyme to change its shape upon substrate binding represents the concept of _____. A) lock and key B) induced fit C) proximity and orientation effects D) covalent catalysis E) none of the above
B) Induced fit
Conversion of factor X to factor Xa represents a(n) _____ form of activation; binding of antithrombin to thrombin represents a(n) _____ form of inhibition. A) reversible; reversible B) irreversible; reversible C) reversible; irreversible D) irreversible; irreversible E) none of the above since antithrombin is not an inhibitor of thrombin
B) Irreversible; reversible
The Michaelis constant is defined as _____. A) KM = k2 / k1 B) KM = (k2 + k-1) / k1 C) KM = (k2 - k-1) / k1 D) KM = (k2 + k1) / k-1 E) KM = (k2 - k1) / k-1
B) KM = (k2 + k-1) / k1
Chymotrypsin catalyzes the hydrolysis of peptide bonds adjacent to _____ residues in a peptide. A) neutral polar B) nonpolar C) negatively charged D) positively charged E) all of the above since chymotrypsin has little substrate specificity
B) Nonpolar
What type of inhibition explains why even at very high substrate concentrations, enzyme activity will decrease as time increases? A) allosteric inhibition B) product inhibition C) transition state analogs D) irreversible inhibition E) uncompetitive inhibition
B) Product inhibition
The ability for an enzyme to pick out one particular substrate from the myriad of molecules floating around its environment is an example of _____. A) natural selection B) specificity C) high affinity D) processivity E) none of the above
B) Specificity
Some irreversible inhibitors are called _____ because they bind to the active site of the enzyme and begin the catalytic process, just like a normal substrate. A) irreversible substrates B) suicide substrates C) noncompetitive substrates D) ping pong substrates E) allosteric substrates
B) Suicide substrates
During the first half of the chymotrypsin mechanism where the acyl-enzyme intermediate is formed, what role does His play? A) general acid only B) general base only C) general acid then general base D) general base then general acid E) nucleophile
D) General base then general acid
Which of the following amino acids would be most likely found in the active site of an enzyme that uses acid-base catalysis? A) Asn B) Ser C) Met D) His E) Trp
D) His
When the transition state is formed, what is the specific interaction observed between Asp and His that helps stabilize the transition state? A) dipole-dipole interaction B) electrostatic interaction C) hydrogen bond D) low-barrier hydrogen bond E) covalent bond
D) Low-barrier hydrogen bond
If a Lineweaver-Burk plot was made for an enzyme-catalyzed reaction, both with and without a competitive inhibitor present, what difference would be seen? A) the y-intercept would be lower for the inhibited reaction B) the y-intercept would be higher for the inhibited reaction C) the slope would be less for the inhibited reaction D) the slope would be greater for the inhibited reaction E) none of the above
D) The close would be greater for the inhibited reaction
The highest point in a reaction coordinate diagram represents _____. A) an intermediate of the reaction pathway B) the reactants in an exergonic reaction C) the products in an endergonic reaction D) the transition state E) the overall G for the reaction
D) The transition state
How are the kinetics of an enzyme-catalyzed reaction affected by a competitive inhibitor? A) Vmax decreased, KM increased B) Vmax decreased, KM decreased C) Vmax decreased, KM unchanged D) Vmax unchanged, KM increased E) Vmax unchanged, KM decreased
D) Vmax unchanged, KM increased
The molecule chymotrypsinogen is known as a(n) _____. A) apoenzyme B) holoenzyme C) protease inhibitor D) zymogen E) none of the above
D) Zymogen
Which of the following must be true for an enzymatic reaction obeying the Michaelis-Menten equation to reach 3/4 of its maximum velocity? A) [S] must be ¾KM B) [S] must be 1.5KM C) [S] must be 2KM D) [S] must be 3KM E) [S] must be 4KM
D) [S] must be 3KM
When is KM considered to be the same as the dissociation constant for the ES complex i.e., KM [E] [S] / [ES]. A) ES → E + P is fast compared to ES → E + S B) the turnover number is very large C) kcat/KM is near the diffusion-controlled limit D) k2 << k-1 E) KM can never be the same as the dissociation constant
D) k2 << k-1
What does the KI for a competitive inhibitor mean? A) higher KI values mean tighter binding to ES complex B) lower KI values mean tighter binding to ES complex C) higher KI values mean tighter binding to the enzyme D) lower KI values mean tighter binding to the enzyme E) KI values tell nothing about inhibitor binding
D) lower KI values mean tighter binding to the enzyme
If a Lineweaver-Burk plot was made for an enzyme-catalyzed reaction, both with and without a noncompetitive inhibitor present, what difference would be seen? A) the y-intercept would be higher with slope unchanged for the inhibited reaction B) the y-intercept would be lower with larger slope for the inhibited reaction C) the y-intercept would be lower with smaller slope for the inhibited reaction D) the y-intercept would be higher with larger slope for the inhibited reaction E) the y-intercept would be higher with smaller slope for the inhibited reaction
D) the y-intercept would be higher with larger slope for the inhibited reaction
Which of the following expresses the velocity for an enzyme-catalyzed reaction that obeys Michaelis-Menten kinetics? A) v = k1[E][S] B) v = k1[E][S] - k-1[ES] C) v = k1[E][S] + k2[ES] D) v = k2[ES] E) v = k2[ES] - k-1[ES]
D) v = k2[ES]
If an enzyme rate increases 10-fold for every 5.7 kJ/mol decrease in the energy of activation, what rate increase would be observed if three H-bonds were stabilizing the transition state with each H-bond having a strength of 21 kJ/mol? A) 11-fold increase B) 37-fold increase C) 60-fold increase D) 100-fold increase E) 1011-fold increase
E) 1011-fold increase
If an enzyme-catalyzed reaction with a KM of 3.5 mM has a velocity of 5 mM/min at a substrate concentration of 0.5 mM, what is the Vmax? A) 0.625 mM/min B) 15 mM/min C) 17.5 mM/min D) 35 mM/min E) 40 mM/min
E) 40 mM/min
The individual hemoglobin subunits and myoglobin share similar ___________ structure but have different ____________ structure.
Secondary and tertiary; primary
The ability for an enzyme to pick out one particular substrate from the myriad of molecules floating around its environment is an example of ___________.
Specificity
The highest point in a reaction coordinate diagram represents ________________.
The transition state
Which protein in the blood is responsible for converting fibrinogen to fibrin?
Thrombin
Of all the species that enzymes bind, they are thought to bind the most tightly to ________________.
Transition states
With respect to oxygen saturation, hemoglobin is ___________ saturated at the pO2 of the lungs and ___________ saturated at the pO2 of the tissue.
>90%; between 30 and 70%
An uncatalyzed reaction has a rate of 4.2 x 10-7 sec-1. When an enzyme is added the rate is 3.2 x 104 sec-1. Calculate the rate enhancement caused by the enzyme. A) 7.6 x 1010 B) 3.2 x 104 C) 1.3 x 10-2 D) 7.4 x 10-3 E) cannot be determined
A) 7.6 x 1010
During the formation of microfilaments, which of the following occurs? A) ATP hydrolysis is catalyzed by f-actin. B) F-actin polymerizes, becoming g-actin. C) None of these choices. D)ATP binds to f-actin. E) Polymerization proceeds quickly at first, then slows after about ten actin monomers have polymerized.
A) ATP hydrolysis is catalyzed by f-actin
What is an example of a conservative amino acid substitution?
Ile > Leu
What is the most effective way to increase the rate of a biochemical reaction?
Add a catalyst
The enzyme hexokinase catalyzes a reaction where its substrates are completely sequestered from the aqueous environment allowing for interactions to occur between enzyme and substrates that would not normally occur in an aqueous environment. What term describes this type of catalysis? A) electrostatic catalysis B) desolvation catalysis C) non-aqueous catalysis D) hydrogen-bonded catalysis E) closed-system catalysis
A) Electrostatic catalysis
When a substrate and enzyme interact, the first chemical species formed is _____. A) enzyme-substrate complex B) enzyme-transition state complex C) enzyme-product complex D) enzyme plus product E) none of the above
A) Enzyme-substrate complex
How does a catalyst affect the overall G of an endergonic reaction? A) it has no effect B) the reaction becomes more endergonic C) the reaction has a G of zero D) the reaction becomes exergonic E) none of the above
A) It has no effect
A reversible inhibitor that binds to a site other than the active site regardless of whether or not the substrate is bound is a _____. A) noncompetitive inhibitor B) competitive inhibitor C) uncompetitive inhibitor D) allosteric inhibitor E) suicide substrate
A) Noncompetitive inhibitor
In a bisubstrate reaction, reactant A binds, followed by reactant B which then get converted to products C and D. An experiment showed that B cannot bind without A having bound first. What mechanism is indicated by this data? A) ordered mechanism B) random mechanism C) ping pong mechanism D) cooperative mechanism E) none of the above
A) Ordered mechanism
What amino acid performs the nucleophilic attack during the chymotrypsin mechanism? A) Ser B) His C) Lys D) Cys E) Thr
A) Ser
Which protein in the blood is responsible for converting fibrinogen to fibrin? A) thrombin B) factor X C) factor VII D) factor VIIa E) prothrombin
A) Thrombin
In an enzyme mechanism that generates a negative charge in the transition state, which of the following would be most effective to have in the active site of the enzyme? A) transition metal cation B) Asp residue C) Gln residue D) transition metal anion E) none of the above
A) Transitional metal cation
How are the kinetics of an enzyme-catalyzed reaction affected by a mixed inhibitor? A) Vmax decreased, KM increased or decreased B) Vmax decreased, KM decreased C) Vmax decreased, KM increased D) Vmax unchanged, KM increased E) Vmax unchanged, KM increased or decreased
A) Vmax decreased, KM increased or decreased
A Lineweaver-Burk plot is a _____. A) double reciprocal plot B) Michaelis-Menten plot C) sigmoidal plot D) hyperbolic plot E) logarithmic plot
A) double reciprocal plot
In the chymotrypsin mechanism, what is used to stabilize the negative charge on the carbonyl oxygen of the transition state? A) hydrogen bonding between the enzyme and the anion from the carbonyl oxygen B) electrostatic interaction of the positively charged His and carbonyl oxygen C) electrostatic interaction of the negatively charged Asp and carbonyl oxygen D) electrostatic interaction of the active site Zn2+ and carbonyl oxygen E) all of the above
A) hydrogen bonding between the enzyme and the anion from the carbonyl oxygen
The catalytic constant, or kcat, is also known as the _____. A) turnover number B) saturation number C) catalytic efficiency number D) diffusion number E) Menten number
A) turnover number
Which of the following properly expresses the Michaelis-Menten equation? A) vo = Vmax [S] / (KM + [S]) B) vo = Vmax KM / (KM + [S]) C) kcat = Vmax / [E]T D) Vmax = vo [S] / (KM + [S]) E) Vmax = vo KM / (KM + [S])
A) vo = Vmax [S] / (KM + [S])
A reversible inhibitor that only affects multisubstrate enzymes and binds to the enzyme only after one substrate has bound is a _____. A) noncompetitive inhibitor B) uncompetitive inhibitor C) competitive inhibitor D) allosteric inhibitor E) suicide substrate
B) Uncompetitive inhibitor
Of the following ions, which would be most likely to participate in metal ion catalysis? A) Na+ B) Zn2+ C) Ag+ D) K+ E) Ba2+
B) Zn2+
An extremely efficient enzyme has a _____ KM and a _____ kcat. A) small; small B) small; large C) large; large D) large; small E) kcat and KM do nothing to predict the efficiency of an enzyme
B) small; large
If a Lineweaver-Burk plot gave a line with an equation of y = 0.25 x + 0.34, what are the values of KM and Vmax if the substrate concentration is in mM and the velocity in mM/s? A) 0.085 mM and 0.34 mM/s B) 2.9 mM and 0.023 mM/s C) 0.74 mM and 2.9 mM/s D) 0.37 mM and 1.4 mM/s E) 1.35 mM and .034 mM/s
C) 0.74 mM and 2.9 mM/s
What is the kcat for a reaction in which Vmax is 0.4 mmoles/min and the reaction mixture contains 5 10-6 micromoles of enzyme? A) 2 x 10-14 min-1 B) 2 x 10-11 min-1 C) 8 x 107 min-1 D) 4 x 108 min-1 E) 8 x 109 min-1
C) 8 x 107 min-1
What three amino acids are found in the catalytic triad of chymotrypsin? A) Glu, His, Thr B) Ser, Arg, Cys C) Asp, His, Ser D) Cys, Lys, Glu E) Asn, His, Thr
C) Asp, His, Ser
Which of the following explains how cell division is blocked by drugs that prevent proper microtubule function? A) The condensation of chromatin requires a microtubule skeleton. B) Production of new membranes for organelles and nucleus requires microtubules. C) Chromosomes separate along a microtubule spindle. D) Division of organelles between daughter cells requires organelle movement along microtubules.
C) Chromosomes separate along a microtubule spindle.
Which of the following is true about enzymes? A) enzymes show very little specificity for their substrates B) enzymes catalyze reactions in only one direction C) enzyme activities can often be regulated D) enzymes reaction rates are generally slower than other chemical catalysts E) enzymes operate under a wide range of temperatures and pH
C) Enzyme activities can often be regulated
Chymotrypsin has a large specificity pocket to bind the aromatic amino acids while elastase has a very small specificity pocket meant to bind Ala or Gly. Which of the following amino acid substitutions changes the specificity pocket of chymotrypsin to that of elastase? A) Trp --> Ser B) Leu --> Ala C) Gly --> Val D) Lys --> Asp E) Val --> Asn
C) Gly --> Val
Chymotrypsin catalyzes the hydrolysis of a peptide bond and is therefore categorized as a _____. A) oxidoreductase B) transferase C) hydrolase D) lyase E) ligase
C) Hydrolase
How does a catalyst increase the rate of a reaction? A) it makes the reaction more exergonic B) it increases the temperature of the reaction C) it allows reacting molecules to more easily form the transition state D) it causes a localized increase in the concentration of reactants E) none of the above
C) It allows reacting molecules to more easily form the transition state
In the enzyme catalyzed decarboxylation of acetoacetate, a Schiff base is formed between the ketone of acetoacetate and a _____ residue in the active site of the enzyme. A) Arg B) Asn C) Lys D) Glu E) Ser
C) Lys
In a bisubstrate reaction, reactant A binds and is then converted to product C. Next, reactant B binds and is then converted to product D. An experiment showed that B cannot bind without C being released first. What mechanism is indicated by this data? A) ordered mechanism B) random mechanism C) ping pong mechanism D) cooperative mechanism E) none of the above
C) Ping pong mechanism
Which of the following occurs in hemoglobin upon oxygen binding? A) Hemoglobin changes from the R state to the T state. B) The heme Fe2+ is pulled out of the plane of the heme group. C) The central cavity between the four subunits is decreased in size. D) The His coordinated to the heme Fe2+ is pushed away from the heme group.
C) The central cavity will decrease in size
Zymogens are not enzymatically active because _____. A) they do not contain the cofactors required for catalysis B) they are the product of mutated genes C) their active sites are distorted and incapable of enzymatic activity D) the pH of their environment is not optimal for activity E) none of the above
C) Their active sites are distorted and incapable of enzymatic activity
Of all the species that enzymes bind, they are thought to bind most tightly to _____. A) substrates B) products C) transition states D) intermediates E) all are bound very tightly
C) Transition states
How is an enzyme-catalyzed reaction affected by the addition of more enzyme? A) velocity is not effected B) velocity will increase only if more substrate is also added C) velocity will increase D) velocity will decrease E) none of the above
C) Velocity will increase
How are the kinetics of an enzyme-catalyzed reaction affected by a purely noncompetitive inhibitor? A) Vmax decreased, KM increased B) Vmax decreased, KM decreased C) Vmax decreased, KM unchanged D) Vmax unchanged, KM increased E) Vmax unchanged, KM decreased
C) Vmax decreased, KM unchanged
Which of the following represents a rapid and reversible mechanism to alter the activity of an enzyme? A) synthesis of more enzyme to increase activity B) degradation of enzyme to decrease activity C) covalent attachment of a phosphate group to increase or decrease activity D) movement of an enzyme from one cellular compartment to another E) none of the above
C) covalent attachment of a phosphate group to increase or decrease activity
The idea that binding of one molecule of oxygen to hemoglobin enhances further binding of oxygen to hemoglobin is called ___________.
Cooperativity
An enzyme that forms a covalent bond with its substrate during the course of a reaction is considered to undergo ____________.
Covalent catalysis
What fiber is paired with this protein that forms it: Tubulin
Microtubules: tubulin
Which of the following is a feature of protease inhibitor specific for trypsin? A) contains a positive charge to mimic the charge of the substrate B) ability to interact with the Ser of the catalytic triad C) inability to form the tetrahedral intermediate D) high affinity for the enzyme active site E) all of the above
E) All of the above
Which of the following is seen in a reaction coordinate diagram for an enzyme-catalyzed reaction that uses covalent catalysis? A) an intermediate B) two distinct transition states C) reactants that are lower in energy than an intermediate D) products that are lower in energy than an intermediate E) all of the above
E) All of the above
Which of the following is true regarding heparin? A) it is an allosteric activator of antithrombin B) it is a sulfated polysaccharide C) it simultaneously binds to antithrombin and the target of antithrombin D) it is used clinically as an anticoagulant E) all of the above
E) All of the above
Which of the following is true regarding transition state analogs? A) they are competitive inhibitors B) they bind to an active site with much higher affinity than most inhibitors C) they are much more stable than the transition state D) their affinity for an enzyme is often much greater that the substrate E) all of the above
E) All of the above
Which of the following statements regarding allosteric enzymes is true? A) they are always oligomeric B) they are generally found at regulatory sites in metabolic pathways C) they are subject to regulation by both positive and negative effectors D) a plot of velocity versus [substrate] often yields a sigmoidal curve E) all of the above
E) All of the above
Which of the following types of enzyme-catalyzed reactions follows non-Michaelis-Menten kinetics? A) bisubstrate reactions with a random mechanism B) bisubstrate reactions with a ping pong mechanism C) bisubstrate reactions with an ordered mechanism D) allosteric enzyme reactions E) all of the above
E) All of the above
What amino acid residue present in the specificity pocket allows trypsin to bind to peptides containing Arg or Lys? A) Ser B) His C) Lys D) Val E) Asp
E) Asp
An inhibitor that binds to the active site only in the absence of the substrate and in a reversible fashion is a(n) _____. A) allosteric inhibitor B) suicide substrate C) mixed inhibitor D) noncompetitive inhibitor E) competitive inhibitor
E) Competitive inhibitor
Different enzymes that catalyze the same reaction are known as _____. A) transferases B) isomerases C) allosteric enzymes D) holoenzymes E) isozymes
E) Isozymes
An organic molecule that is tightly bound to an enzyme and participates in an enzyme catalyzed reaction is specifically referred to as a _____. A) cofactor B) metal ion C) coenzyme D) cosubstrate E) prosthetic group
E) Prosthetic group
For a reaction A + B → C, if [B] is much larger than [A] so that [B] essentially remains constant over the course of the reaction, the kinetics will be _____. A) zero-order B) hyperbolic C) first-order D) sigmoidal E) pseudo first-order
E) Pseudo first-order
Which of the following must be true if the steady state assumption is to be used? A) [E]T = [ES] B) (k2 - k-1) / k1 = 1 C) k1[E][S] = k2[ES] D) k1[E][S] = k2[ES] - k-1[ES] E) d[ES] / dt = 0
E) d[ES] / dt = 0
Which of the following indicates that an enzyme has evolved to its most efficient form? A) kcat is a large number B) KM is a small number C) KM is a large number D) kcat/KM is a small number E) kcat/KM is near the diffusion-controlled limit
E) kcat/KM is near the diffusion-controlled limit
When oxygen is bound to the heme group of myoglobin, it is coordinated between ____________ and ___________.
E7 His; Fe2+ of heme
What fiber is paired with this protein that forms it: Collagen?
Extracellular support fibers: collagen
What amino acid would most likely be found in the active site of an enzyme that uses acid-base catalysis?
His
Ascorbic acid is required for the production of __________ in collagen.
Hydroxyproline
What fiber is paired with this protein that forms it: Keratin
Intermediate filaments: keratin
What fiber is paired with this protein that forms it: Actin?
Microfilaments: actin
