Ch 13 Questions, Garrett Chapter 15, Garrett Chapter 14, GARRETT Exam 3
if the rate constant for the enzyme catalyzed reaction is 2*10^5/sec and the rate constant for the uncatalyzed reaction 2*10^-6/sec, the catalytic power of the enzyme is
10^11
if an enzyme has a Vmax of 15 mM/min, what is the velocity if the substrate is present at 1/5 the Km
2.5 (nM/min)
an enzymatic reation has a Vmax of 30 uM/min and a Km of 50 uM. if the concentration of the substrate is 25 uM what is velocity
20 (uM/min)
for an enzyme-catalyzed reaction, the initial velocity was determined at two different concentrations of the substrate. which of the following would be the closest to Vmax [S] = 1, 4 [V] = 2, 2.8
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 Km [S] = 1, 4 [V] = 2, 2.8
0.6 (mM)
All are catalytic mechanisms or factors that contribute to the performance of enzymes EXCEPT: A. entropy gain in ES formation. B. covalent catalysis. C. general acid or base catalysis. D. proximity and orientation. E. all are true.
A
All are true for the effect of protons on binding of O2 by hemoglobin EXCEPT: A. The saturation curve of Hb for O2 is displaced to the left (greater binding) as acidity increased. B. Actively metabolizing tissues produce acid which is an antagonist of oxygen binding by Hb. C. As the pH decreases, dissociation of O2 from Hb is enhanced. D. The phenomenon is called the Bohr Effect. E. All are true.
A
BPG shifts the oxygen saturation curve of Hb to the ____ because BPG binds to ____ making Hb an O2 delivery system eminently suited for ____. A. right; deoxyHb; humans and other primates B. right; deoxyHb; cattle, sheep and goats C. left; oxyHb; cattle, sheep and goats D. left; oxyHb; humans and other primates E. none of the above
A
Fetal hemoglobin (Hb F) has an intrinsically greater affinity for O2 than adult hemoglobin (Hb A) because: A. Hb F has a diminished capacity to bind BPG compared to Hb A. B. Hb A has a greater affinity for oxygen than does Hb F. C. BPG binds Hb F with greater affinity than it binds Hb A. D. The pH of fetal blood is less than the pH of maternal blood. E. All of the above are correct.
A
For muscle glycogen phosphorylase, Pi (inorganic phosphate) is a: A. positive homotropic effector. B. negative homotropic effector. C. positive heterotropic effector. D. negative heterotropic effector. E. none of the above
A
In the hydrolysis of p-nitrophenylacetate by chymotrypsin all of the following are correct EXCEPT: A. the first product is acetic acid. B. an acetyl-enzyme intermediate forms during the mechanism. C. attack of a water molecule on the acyl-enzyme intermediate yields the second product. D. the active site contains a serine residue, an unprotonated histidine, and an unprotonated aspartate residue at pH 7.0 prior to binding the substrate. E. none of the above.
A
Most covalent catalysis is carried out by enzymes using a: A. ping-pong kinetic mechanism. B. sequential bisubstrate kinetic mechanism. C. random bisubstrate kinetic mechanism. D. simple unimolecular kinetic mechanism. E. none of the above.
A
Nucleophilic centers for covalent catalysis include all of the following amino acid side-chains in proteins EXCEPT: A. methyl. B. amines. C. carboxylate. D. aryl and alkyl hydroxyls. E. thiols.
A
Proinsulin is converted into insulin by: A. proteolytic excision of a specific peptide. B. allosteric binding of glucose. C. phosphorylation to the active form. D. removal of phosphate by converter enzymes. E. none of the above.
A
The T form (tense or taut form) of deoxyhemoglobin differs from oxyhemoglobin (the R form or relaxed form) by all EXCEPT: A. covalent linkages between subunits. B. specific intrachain hydrogen bonds. C. between b-subunit salt links (ion-pair bonds). D. between a-subunits salt links (ion-pair bonds). E. intrachain salt bridges.
A
The catalytic triad common to many serine proteases involves shuttling of protons between (sequence in the catalytic triad): A. ser-his-asp B. his-ser-asp C. ser-his-his D. ser-asp-his E. cys-his-ser
A
The good transition state analog is one which would serve also as an effective: A. competitive inhibitor. B. noncompetitive inhibitor. C. allosteric inhibitor. D. mixed-noncompetitive inhibitor. E. irreversible inhibitor.
A
The initial bond formation in the covalent intermediate in the chymotrypsin catalyzed reaction is between: A. serine and the carbonyl carbon in the peptide backbone. B. serine and the nitrogen in the peptide backbone. C. histidine and the carbonyl carbon in the peptide backbone. D. histidine and the nitrogen in the peptide backbone. E. aspartate and the carbonyl carbon in the peptide backbone
A
Usually the quickest method of influencing an enzymatic activity is by: A. allosteric regulation. B. covalent modification. C. enzyme induction. D. activation of a zymogen. E. enzyme destruction.
A
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 y = 1.1x + 0.2. which of the following statements is true a. inhibition if competitive b. inhibition of noncompetitive c. inhibition is uncompetitive d. Vmax has decreased e. Km has decreased
A. inhibition is competitive
Adenylyl cyclase catalyzes the synthesis of cAMP, and cAMP hydrolysis is catalyzed by a 5'-phosphodiesterase. If caffeine inhibits 5'-phosphodiesterases, drinking a caffeinated beverage would ____ cAMP levels and ____ glycogen phosphorylase activity. A. increase; decrease B. increase; increase C. decrease; decrease D. decrease; increase E. have no effect; have no effect
B
All are true about isozymes of lactate dehydrogenase (LDH) that are present in a number of different tissues EXCEPT: A. They have differing Km values for lactate. B. The amount of subunit phosphorylation differs. C. They have differing Km values for pyruvate. D. The ratios of A and B subunits differ depending upon the tissue type E. They have different kinetic parameters.
B
All of the following are characteristics of hemoglobin's binding of oxygen EXCEPT: A. CO2 promotes dissociation of O2 from hemoglobin by lowering the pH. B. Protons promote binding of oxygen by Hb. C. 2,3-Bisphosphoglycerate (BPG) promotes release of O2 by Hb. D. CO2 can bind with Hb's free amino groups and stabilize deoxy-Hb. E. BPG and O2 are mutually exclusive allosteric effectors of Hb
B
All of the following are examples of a zymogen and its activating protease EXCEPT: A. chymotrypsinogen and chymotrypsin. B. procarboxypeptidase and elastase. C. proelastase and elastase. D. pepsinogen and pepsin. E. trypsinogen and trypsin.
B
Enzymes have active sites which have the greatest complementarity to the: A. substrate. B. transition state. C. product. D. both substrate and product. E. none of the above
B
HIV-1 protease is different from most mammalian aspartic acid proteases in that it has: A. two subunits each with a two-aspartate active site. B. two subunits each contributing an aspartate to the active site. C. two active sites on one protein. D. two subunits, one with an active site, and the other with a regulatory activity. E. none of the above.
B
In the chymotrypsin reaction mechanism there is a low-barrier hydrogen bond (LBHB) formed between: A. Asp102 and Ser195. B. Asp102 and His57. C. His57 and Ser195. D. Ser195 and carbonyl oxygen in the peptide bond. E. None of the above.
B
The cause of cell sickling in sickle cell anemia is: A. interaction of oxy-Hb S with the cell membrane. B. precipitation of deoxy-Hb S into long, chain-like fibers. C. formation of oxy-Hb S complexes and subsequent cell disruption. D. precipitation of Hb S - Hb A hybrid molecules. E. none of the above.
B
The correct sequence for the hormone-activated enzymatic cascade that leads to activation of glycogen phosphorylase is: A. Phosphorylation to active phosphorylase kinase B. Activation of G-protein C. Activation of adenylyl cyclase to produce cAMP D. Phosphorylation of glycogen phosphorylase E. cAMP activation of protein kinase A (PKA) A. A, B, C, D, E B. B, C, E, A, D C. C, B, A, D, E D. B, D, E, A, C E. E, A, D, C, B
B
The mechanism of chymotrypsin involves which of the following elements? A. deprotonation of an active site Asp residue by His to start the reaction B. formation of an acyl-enzyme intermediate that must be hydrolyzed to complete the reaction C. stabilization of the positively charged His by a Gln residue D. direct deprotonation of water by His to generate a hydroxide ion for initiation of the reaction E. both a and b occur
B
When binding one equivalent of S to an allosteric protein enhances the binding of additional equivalents of S to the same protein molecule, it is termed a(n): A. negative heterotropic effector. B. positive homotropic effector. C. positive heterotropic effector. D. negative homotropic effector. E. none of the above.
B
Which of the following statements regarding enzymes and transition states is true? A. stabilization of the transition state must be less than stabilization of ES for catalysis to occur B. binding of substrate to an enzyme often causes strain, thus promoting transition state formation C. the transition state conformation of an enzyme catalyzed reaction is identical to the conformation seen in the uncatalyzed transition state D. formation of the transition state always assures that the reaction will proceed to product E. none of the above are true
B
All are characteristic of allosteric enzymes EXCEPT: A. Effectors may show stimulatory or inhibitory activity. B. They have multiple subunits. C. They obey Michaelis-Menten kinetics. D. The regulatory effect is by altering conformation and interaction of subunits. E. Binding one subunit impacts binding of substrate to other subunits.
C
Because the enzymatic reaction rate is determined by the difference in energy between ES and ____, the tighter binding of the substrate, the ____ the rate of reaction. A. S; higher B. P; lower C. EX ; lower D. EX ; higher E. S; lower
C
Effective HIV-1 protease inhibitors should have all of the following characteristics EXCEPT: A. effective delivery in sufficient quantities to the desired site(s) of action in the organism. B. relative specificity for the HIV-1 protease. C. a backbone -OH group that forms a weak association with the two active-site carboxyl groups of the protease. D. results in inhibiting the production of new virus particles in cells of infected patients. E. broad spectrum enough to be effective against mutant viral forms.
C
For the K system of the MWC model, the half-maximum velocity (K0.5) ____ in response to effectors, Vmax ____, and K system enzymes are adopted to conditions when prevailing [S] is ____. A. remains constant; remains constant; rate limiting B. remains constant; changes; saturating C. changes; remains constant; rate limiting D. changes; changes; saturating E. changes; remains constant; saturating
C
Regulation of metabolism by activation of the gene encoding a particular enzyme is called ____. A. covalent modification B. repression C. induction D. allosteric activation E. none of the above
C
The Ga subunit of GTP-binding protein (G protein) has all of the following characteristics EXCEPT: A. activates adenylyl cyclase. B. hormone-receptor complex promotes Ga release from Gbg. C. has a very active GTPase activity. D. binds GDP in the Gabg complex. E. GTP hydrolysis leads to Ga-adenylyl cyclase dissociation.
C
The function of glycogen phosphorylase is: A. the conversion of glucose-1-phosphate to glucose-6-phosphate. B. to break down ATP. C. to catalyze the phosphorolysis of glucose-1-phosphate from glycogen molecules. D. to inhibit the production of glucose-1-phosphate. E. to stimulate the build up of glycogen.
C
We are protected to some extent against low level CO poisoning because: A. His F8 on Hb distorts the heme iron atom out of the heme plane and attracts O2, but not CO. B. Affinity of Hb for O2 is much greater than for CO. C. His E7 blocks perpendicular binding of CO to heme iron allowing for better binding competition by O2. D. The competition of O2 for heme is much greater than CO for heme. E. None of the above.
C
Which of the following statements regarding enzyme regulation is true? A. addition of an inhibitor to a V system results in kinetics similar to addition of a competitive inhibitor to a typical hyperbolic system B. allosteric effectors are always more powerful than covalent modification C. addition of an allosteric activator to a K system changes the plot of V vs. [S] from a sigmoidal curve to a more hyperbolic curve D. the T state of an enzyme generally has more activity than the R state E. none of the above are true
C
Which statement below about contrasting Hb and Mb is FALSE? A. Hb shows sigmoidal, whereas Mb shows hyperbolic oxygen saturation curves. B. Hb shows cooperativity, whereas Mb does not. C. Hb binds O2 more tightly than Mb. D. Oxygen binds to a ferrous ion in both proteins. E. Hb-oxygen binding is dependent on physiological changes in pH, whereas Mb-oxygen binding is not.
C
All are properties of regulatory enzymes EXCEPT: A. pathway end-products may act as allosteric inhibitors. B. v vs [S] plots are sigmoid- or S-shaped. C. substrate binding is cooperative. D. monomeric enzymes with a single regulated active site. E. may be stimulated by allosteric activators.
D
Aspartate proteases display a variety of substrate specificities, but normally they are most active in cleavage of peptide bonds: A. on the carboxyl side of the basic amino acids. B. on the carboxyl side of aromatic amino acids. C. on the carboxyl side of small, neutral residues. D. between two hydrophobic amino acid residues. E. none of the above.
D
Carbon dioxide affects O2 binding to Hb by: A. Hb competing with carbonic anhydride for CO2. B. directly binding to heme-Fe in the oxygen binding site. C. forming iron carbonate with the heme-iron. D. forming H+ + HCO3- where the H+ is an antagonist to oxygen binding to Hb. E. forming HCO3- that combines with H+ to increase CO2 binding
D
Glycogen phosphorylase displays allosteric activation and inhibition by multiple modes. Which of the following is a correct relation? A. phosphate: positive heterotropic effector B. AMP: negative heterotropic effector C. ATP: positive heterotropic effector D. glucose-6-phosphate: negative heterotropic effector E. phosphorylation: covalent inhibitor
D
Organic fluorophosphates are ____ inhibitors of serine proteases such as chymotrypsin, etc. A. competitive B. uncompetitive C. noncompetitive D. irreversible E. mixed noncompetitive
D
The catalytic mechanism below is an example of: A. covalent nucleophilic catalysis. B. covalent electrophilic catalysis. C. specific base catalysis. D. general base catalysis. E. low barrier hydrogen bond catalysis.
D
The enzyme-catalyzed reaction rate will be increased if the energy level of ES can be increased by all EXCEPT: A. destabilization of ES by strain. B. loss of entropy due to binding of E and S. C. destabilization of ES by distortion. D. destabilization of ES by solvation. E. destabilization of ES by electrostatic effects.
D
The mechanism of aspartate protease catalysis is proposed to be: A. covalent nucleophilic catalysis. B. covalent electrophilic catalysis. C. specific base catalysis. D. general base-general acid catalysis facilitated by a low barrier hydrogen bond. E. all of the above
D
The polypeptide of myoglobin serves all of the following functions EXCEPT: A. protects the heme iron from oxidation. B. cradles the heme group. C. provides a pocket for O2 to fit. D. keeps the heme iron in the ferric form. E. none of the above.
D
The presence of a negative allosteric effector on an allosteric protein would: A. cause a shift to the left in the sigmoidal curve. B. increase the number of R conformations. C. decrease the cooperativity of the substrate. D. raise the apparent value of the equilibrium constant, L. E. increase the likelihood of the binding of S.
D
The transition state has an estimated life-time of about: A. microseconds (10-6 s). B. nanoseconds (10-9 s). C. (10-2 s). D. (10-14 to 10-13 s). E. milliseconds (10-3 s).
D
When O2 binds to ____ in Hb, the ____ ion is drawn into the plane of the ____ causing a conformational change that is transmitted to adjacent subunits enhancing the ____ for additional O2 binding. A. porphyrin; Mg; globin; planarity B. porphyrin; Fe; heme; folding C. heme; Mg; globin; attraction D. heme; Fe; porphyrin; affinity E. Fe; CO; porphyrin; affinity
D
All are true for cAMP-dependent protein kinase EXCEPT: A. also known as PKA. B. phosphorylase kinase is a substrate. C. consists of a pair of catalytic subunits. D. two regulatory subunits block catalytic activity without cAMP binding. E. phosphorylates glycogen phosphorylase
E
All are true for low-barrier hydrogen bonds EXCEPT: A. The hydrogen is centered between the two heteroatoms. B. The interactions are more covalent. C. The bond order approaches 0.5 for both O-H interactions. D. The barrier that the hydrogen atom must surmount to exchange oxygens becomes lower. E. All are true.
E
All are true for the enzyme-transition state complex EXCEPT: A. It is designated as EX . B. The enzyme stabilizes the transition-state complex more than it stabilizes the substrate complex. C. The enzyme is "designed" to bind the transition-state structure more tightly than the substrate or product. D. The energy barrier between ES and EX is less than the energy barrier between S and X . E. All are true.
E
All of the following are correct statements about enzyme regulation EXCEPT: A. Enzymes can be inhibited by the products they produce. B. Enzymes can be inactivated by the addition of a functional group. C. Coenzyme and substrate availability can regulate enzyme reaction rate. D. The reaction rate slows as equilibrium is approached. E. The activity of an enzyme is covalently affected by allosteric regulators.
E
An enzyme that displays negative cooperativity has ____ activity when the substrate is present at concentrations ____ than the value of K0.5 when compared with enzymes that display no cooperativity. A. increased; greater B. increased; less C. decreased; greater D. decreased; less E. both b and c are correct
E
Because the pKa is near 7, ____ side-chains are often involved in general acid-base catalysis. A. cysteine B. aspartate C. glutamate D. lysine E. histidine
E
Characteristics of glycogen phosphorylase include all EXCEPT: A. covalently linked pyridoxal phosphate. B. an active site at the center of each of two identical subunits. C. regulatory phosphorylation site on a Ser residue. D. allosteric effector sites for ATP and glucose-6-phosphate. E. all are true.
E
Metal ion catalysis include all EXCEPT: A. increased acidity of a nucleophile with an ionizable proton. B. metal ion requirement to maintain the stable, native state of the enzyme. C. metal binding weakly, perhaps only during the catalytic cycle. D. electrophilic catalysis, stabilizing the increased electron density or negative charge that can develop during a reaction. E. all are true.
E
Since enzymes are not rigid molecules but rather flexible proteins, which of the following may be attributed to this fact? A. active sites are able to conform to the shape of the substrate B. catalytic residues are oriented in such as way to aid in bond breakage and bond formation C. strain is placed upon the substrate while it binds to the enzyme D. near-attack conformations are achieved during formation of the transition state during an enzyme catalyzed reaction E. all of the above are correct
E
Transition-state analogs are: A. approximations of the transition state that bind more tightly than the substrate. B. compounds that compete for the active site, but are not necessarily very similar to the substrate. C. stable molecules that can not be expected to resemble the true transition state too closely. D. stable chemically and structurally similar molecules to the transition state. E. all of the above.
E
Which of the following are relevant to the reaction catalyzed by chorismate mutase? A. the reaction involves a concerted intramolecular rearrangement of chorismate to prephenate during the synthesis of phenylalanine. B. the enzyme catalyzed and uncatalyzed reactions follow almost identical routes C. the enzymatic reaction is thought to involve transition state stabilization by 12 electrostatic and hydrogen bond interactions D. the geometry of the enzyme active site is such that the difference in energy between ES and the near attack conformation is less than 1 kJ/mol E. all of the above are true
E
Which of the following statements is correct regarding isozymes? A. they catalyze the same reaction but have vastly different structures B. they are always monomeric proteins C. their differences are based upon the type of tissue in which they are present D. they often respond to different inhibitors and activators E. both c and d are correct
E
in uncompetitiv inhibition a. I combines only with ES b. I combines only with E c. I combines E and ES d. I combines with EP e. none of above
a. (I combines only with ES)
all are true for inhibitor I if it is a competitive inhibitor EXCEPT a. it binds a site other than the active site b. it is structurally similar to the substrate c. EI does not give rise to E + P d. for a given [I] v decreases e. at some point S can displace all of I on E
a. (it binds to a site other than the active site)
which statement is correct about the Michaelis-Menten constant, Km, for the kinetic mechanism below E + S = ES = E + P a. it is numerically equal to the substrate concentration required to achieve one half the maximum velocity b. its defined as Km = k1/(k-1 + k2) c. it is approximately equal to the dissociation constant for the enzyme-substrate complex to E + P d. the value of Km is constant for an enzyme regardless of the specific substrate molecule used to determine it e. its numeric value has the units of moles^-1
a. (it is numerically equal to the substrate concentration required to achieve one half the maximum velocity)
catalytic antibodies, also called ____, are generated against an antigen that is: a. abzymes; an analog of the transition-state intermediate in the reaction. b. abzymes; the substrate of the reaction. c.zymogens; an analog of the product of the reaction. d.holoenzyme; an analog of the transition-state intermediate in the reaction. e.none of the above.
a. abzymes; an analog of the transition-state intermediate in the reaction.
the trivial term for an enzyme that moves a functional group from one place to another on the substrate is _____ a. isomerase b. oxidoreductase c. protease d. kinase e. catalase
a. isomerase
when every enzyme molecule in the reaction mixture has its substrate-binding site occupied by substrate, then kinetics become ____ order, and the velocity is ________ a. zero, Vmax b. first, Vmax c. second, Vmax d. zero, Vmax/2 e. first, Vmax/2
a. zero, Vmax
All are characteristics of ordered single-displacement reactions EXCEPT a. LWB plot with lines that intersect to the left of 1/v axis b. a chemically modified enzyme intermediate c. the lack of any exchange reaction activity d. the lack of competitive substrate effects e. single substrate initial binding activity
b. (a chemical modified enzyme intermediate)
what reaction would NOT proceed via biomolecular elementary steps a. C+D = T+U b. a reaction with rate constant s^-1 c. 2A = D + E d. a reaction with molecularity of 2 e. a reaction with a rate constant in the units of M^-1 s^-1
b. (a reaction with a rate constant in the units of s^-1)
the internation units of an enzyme are based on the a. the ratio of enzyme ot other proteins b. micromoles of product formed per minute c. moles of substrate reacted d. micromoles of product produced at Vmax/2 e. none of above
b. (micromoles of product formed per minute)
all of the following statements are true about the relationships between [S], Km and Vmax EXCEPT: a. as the [S] is increased, v approaches the limiting value, Vmax b. Km = Vmax/2 c. the rate of reaction, v, follows a first order rate equation (v = K'[A] adn K' = Vmax/Km) d. the rate of product formed, v, is at Vmax when [S] >> Km e. Km and Vmax assit in finding the rate of enzyme catalyzed reaction only if the reaction is irreversible
b. Km = Vmax/2
malonate inhibition of succinate dehydrogenase is an example of a. noncompetitive inhibition b. competitive inhibition c. mixed noncompetitive inhibition d. irreversible inhibition e. uncompetitive inhibition
b. competitive inhibition
the catalytically active complex of an apoenzyme and its prosthetic group is referred to a(n) a. catalytic duo b. holoenzyme c. prosthetic enzyme d. dimeric enzyme e. none of above
b. holoenzyme
all of the follwoing statements about noncompeittive inhibition are true EXCEPT: a. they interact with the enzyme as well as the enzyme substrate complex b. increasing [s] can overcome inhibition c. Vmax does not remain the same d. inhibitor can cause conformation change e. inhibitior binds to a different site than does the substrate
b. increasing [s] can overcome inhibition
an enzyme's specificity can be due to a. the ratio of catalyzed rate to the uncatalyzed rate of reaction b. molecular recognition based on structural complementarity c. amount of enzyme produced by the cell d. amount of substrate availabe e. metabolic activator
b. molecular recognition based on structural complementarity
the specific site on the enzyme where ______ binds and catalysis occurs is called the _____ site a. coenzyme, substrate b. substrate, active c. coenzyme, regulatory d. regulatory, active e. none of the above
b. substrate, active
all are characteristics of ribozymes EXCEPT: a.They are critical for removal of introns from mRNA b. They are substrate specific. c.They enhance the reaction rate. d.On the ribosome, they catalyze the peptidyl transferase reaction e. All are true.
e. all are true
which of the following is true regarding the Briggs and Haldane steady state assumption a. it is defined by the equation: E + S = ES = E + P b. it states that the rate of enzyme-substrate complex formation differs from the rate of enzyme-substrate disappearance c. the concentration of enzyme-substrate complex reaches a constant value even in a dynamic system d. the enzyme-substrate complex will always dissociate to form E + P e. the total amount of enzyme is variable, depending on the amount of substrate available
c. (the concentration of the enzyme substrate complex reaches a constant value even in a dynamic system)
the free energy of activation delta G+ is defined as a. the average free energy of the product formed b. the rate of a chemical reaction in relationship to the concentration of reactant molecules c. the energy required to raise the average energy of one mole of reactant to the transition state energy d. the amount of energy released by a spontaneous reaction e. the lowest point on a free energy diagram
c. (the energy required to raise the average energy of one mole of reactant to the transition state energy)
how do catalysts work to accelerate a chemical reaction a. they raise the average energy of the reactants b. they provide a means of acceleration by being completely consumed in the reaction c. they lower energy of activation d. they lower the overall free energy change of the reaction e. they raise the overall free energy change of the reaction
c. (they lower energy of activation)
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 a. slope = Km/Vmax b. y-intercept is 1/Vmax c. x-intercept is 1/Km d. y = 1/V e. x = 1/[S]
c. (x intercept = 1/Km)
all are distinctive features of enzymes EXCEPT: a. regulation b. catalytic activity c. ability to change delta G d. specificity e. none is true
c. ability to change delta G
penicillin and other B lactam antibiotics form a covalent bond to the enzyme glycoprotein transpeptidase. what type of bond is this a. ester b. thioester c. amide d. phosphate e. none of above
c. amide
which of the following statements is NOT characteristic of Kcat/KM a. it corresponds to a second order rate constant b. it provides an excellent parameter for comparison of the catalytic efficiency of enzymes c. it reflects the property of the enzyme when substrate concentration is at saturation d. the upper limit for the kcat/Km value is fixed by the diffusion-controlled limit for reactions which fi 10^9 M^-1 s^-1 e. it is also referred to as the turnover number
c. it reflects the property of the enzyme when substrate concentration is at saturation
Enzymes work by a. providing an alternate reaction pathway b. increasing the spontaneity (delta G) of the reaction c. lowering the activation energy of the reaction d. altering the concentration of the reactants to achieve a favorable delta G e. proceeding in only one direction from reactants to products
c. lowering the activation energy of the reaction
Penicillin is an example of mechanism based enzyme inactivator and is a a. competitive inhibitor b. noncompetitive inhibitor c. suicide substrate d. uncompetitive inhibitor e, none of above
c. suicide substrate
all are true for catalysts EXCEPT: a. they work by lowering the energy of activation b. the average energy of reaction is unchanged c. they combine transiently with the reactants promoting a reactive transition state condition d. they are regenerated after each reaction cycle e. all are true
e. all are true
what is true: a. transition state analog binds covalently to teh enzyme b. noncompetitive inhibitor causes an increase in the Vmax c. presence of a competitive inhibitor can be overcome by addition of more inhibitor d. competitive inhibitor results in a higher apparent Km value e. none of above
d. (competitive inhibitor results in a higher apparent Km value)
All of the following statements about competitive inhibiton are correct EXCEPT: a. competitive inhibitors are often chemical analogs of the substrate b. for a group-specific enzyme, one substrate would be a competitive inhibitor of reactions c. sometimes a product of an enzyme catalyzed reaction is competitive inhibitor of its own production d. in the presence of a competitive inhibitor, the apparent Km would be altered and the Vmax would be decreased e. competitive inhibitors usually interact with the enzyme at the binding site for a substrate
d. (in the presence of a competitive inhibitor, the apparent Km would be altered and Vmax would be decreased)
which of the following statements is true regarding enzyme pathways a. the most effective way to control a pathway is to regulate every enzyme in the pathway b. an enzyme pathway always proceeds in one direction, never in reverse c. a regulatory enzyme is regulated only by molecules within a given pathway d. metabolic pathways are necessary since enzymes usually catalyze only one specific reaction e. none are true
d. metabolic pathways are necessary since enzymes usually catalyze only one specific reaction
all of the following are properties of a coenzyme EXCEPT a. they are usually actively involved in the catalytic reaction of the enzyme b. they tend to be stable in heat c. they can serve as intermediate carriers of functional groups d. they are protein components e. they may contain vitamins as part of their structure
d. they are protein components
all are true of Kcat EXCEPT a. referred to as the molecular activity of the enzyme b. called the turnover number of the enzyme c. measures the maximal catalytic activity or kinetic efficiency of an enzyme d. defines the number of substrate molecules converted into product/enzyme molecule/unit of time when the enzyme is saturated with substrate e. all are true
e. all are true
the pH optimum of an enzyme is a. always between pH 6-8 b. nearly the same for all enzymes c. often dependent upon amino acids that form the active site d. occur when there is optimum secondary and tertiary structure in the active site of the enzyme e. both C and D
e. both C and D
all of the following are true statements about the transition state of the reaction EXCEPT a. the transition state is not an appropriate indication of the rate of reaction b. the transition state is located at the height of the free energy diagram c. the energy required to raise the average energy of one mole of reactant to the transition state is the free energy of activation d. reaching the transition state indicates that there is a high probability that the reaction will occur e. the transition state energy level is the sum of the energy levels of the reactants and products
e. the transition state energy level is the sum of the energy levels of the reactants and products
