Deck 14: Enzyme Regulation

Question 1

Which of the following competes with CoA-SH for binding to E₂PDH?

A)acetyl-CoA
B)NAD⁺
C)NADH
D)ATP

Answer 1

A

Question 2

Which of the following terms describes the regulation of metabolism by activation of the gene encoding a particular enzyme?

A)covalent modification
B)repression
C)induction
D)allosteric activation

Answer 2

C

Question 3

Which of the following statements regarding enzyme regulation is correct?

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 versus [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.

Answer 3

C

Question 4

Which of the following is NOT an example of a zymogen and its activating protease?

A)chymotrypsinogen and chymotrypsin
B)proinsulinc and insulin
C)pepsinogen and pepsin
D)trypsinogen and trypsin

Question 5

Which of the following molecules activates PDH kinase?

A)ADP
B)calcium
C)NADH
D)insulin

Question 6

Which of the following regarding enzyme regulation is correct?

A)The activity of an enzyme is covalently affected by allosteric regulators.
B)Enzymes can be activated by the products they produce.
C)Enzymes can only be inactivated by the addition of a functional group.
D)Coenzyme and substrate availability can regulate enzyme reaction rate.

Question 7

Which of the following is NOT a characteristic of allosteric enzymes?

A)Effectors may show stimulatory or inhibitory activity.
B)They have multiple subunits.
C)They obey Michaelis-Menten kinetics.
D)Binding of 1 subunit impacts binding of substrate to other subunits.

Question 8

For the MWC model,the half-maximum velocity changes in response to effectors.Which of the following explains the reason for this?

A)Vmax remains constant because the [S] is not rate limiting.
B)Vmax changes because the [S] is saturating.
C)Vmax remains constant because the [S] is rate limiting.
D)Vmax changes because the [S] is not saturating.

Question 9

Which of the following terms is used to define the process that occurs when binding 1 equivalent of S to an allosteric protein enhances the binding of additional equivalents of S to the same protein molecule?

A)negative heterotropic effect
B)positive homotropic effect
C)positive heterotropic effect
D)negative homotropic effect

Question 10

Which of the following components of the PDH complex is covalently modified?

A)PDH kinase
B)PDH E1
C)PDH phosphatase
D)PDH E2

Question 11

Which of the following mechanisms is the quickest method of influencing an enzymatic activity?

A)allosteric regulation
B)covalent modification
C)enzyme induction
D)activation of a zymogen

Question 12

Which of the following statements regarding isozymes is correct?

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 metal ions needed for catalysis.
D)They often respond to different inhibitors and activators.

Question 13

Which of the following amino acid residues of the PDH complex is the target of phosphorylation?

A)serine of E1
B)tyrosine of E1
C)serine of E2
D)tyrosine of E2

Question 14

Which of the following is the mechanism by which proinsulin is converted into insulin?

A)by proteolytic excision of a specific peptide
B)by allosteric binding of glucose
C)by phosphorylation to the active form
D)by removal of phosphate by converter enzymes

Question 15

Which of the following is a feature of an enzyme that displays negative cooperativity?

A)Enzyme activity is increased when [S] >>> than the value of K0.5.
B)Enzyme activity is increased when [S] <<< than the value of K0.5.
C)Enzyme activity is decreased when [S] <<< than the value of K0.5.
D)Enzyme activity is unchanged when [S] >>> than the value of K0.5.

Question 16

Which of the following mechanisms describes the function of pyruvate dehydrogenase?

A)to convert glucose-1-phosphate to glucose-6-phosphate
B)to inhibit the production of glucose-1-phosphate
C)to catalyze the conversion of glyceraldehyde into pyruvate
D)to stimulate the breakdown of glycogen

Question 17

Which of the following regarding the isozymes of lactate dehydrogenase,which are present in a number of different tissues is correct?

A)They have similar Km values for lactate.
B)They have different kinetic parameters.
C)The amount of subunit phosphorylation differs.
D)The ratios of A and B subunits are similar in the different tissues.

Question 18

Which of the following is NOT a property of regulatory enzymes?

A)Pathway end products may act as allosteric inhibitors.
B)v versus [S] plots are sigmoid shaped or S shaped.
C)They may be stimulated by allosteric activators.
D)They are monomeric enzymes with a single regulated active site.

Question 19

Which of the following effects does the presence of a negative allosteric effector have on an allosteric protein?

A)causes a shift to the left in the sigmoidal curve
B)increases the number of R conformations
C)decreases the cooperativity of the substrate
D)raises the apparent value of the equilibrium constant,L

Question 20

Which of the following is a characteristic of eukaryotic pyruvate dehydrogenase?

A)It is a complex of 2 enzymes.
B)It is structurally related to succinate dehydrogenase.
C)The active site is at the centre of the 96 subunits.
D)TPP is a required cofactor for E1.

Question 21

When O₂ binds,which of the following components of the heme group is drawn into the plane of the porphyrin,causing a conformational change that is transmitted to adjacent subunits,enhancing the affinity for additional O₂ binding?

A)Mg
B)CO
C)His
D)Fe

Question 22

Which of the following conditions causes cell sickling in sickle cell anemia?

A)interaction of oxyHb S with the cell membrane
B)precipitation of deoxyHb S into long,chain-like fibres
C)formation of oxyHb S complexes and subsequent cell disruption
D)precipitation of Hb S-Hb A hybrid molecules

Question 23

Which of the following components of the eukaryotic PDH complex has the largest number of subunits?

A)lipoate
B)E2
C)TPP
D)E3

Question 24

Why does fetal hemoglobin (Hb F)have an intrinsically greater affinity for O₂ than adult hemoglobin (Hb A)?

A)Hb F has a diminished capacity to bind BPG compared to Hb A.
B)Hb A has more subunits than does Hb F.
C)BPG binds Hb F with greater affinity than it binds Hb A.
D)The pH of fetal blood is lower than the pH of maternal blood.

Question 25

The PDH complex is allosterically activated and inhibited by multiple modes.Which of the following is a correct relation?

A)acetyl-CoA: activation
B)NAD⁺: inhibition
C)NADH: activation
D)CoA-SH: activation

Question 26

Which of the following is NOT a difference between the T form (tense or taut form)of deoxyhemoglobin and the oxyhemoglobin (the R form or relaxed form)?

A)covalent linkages between subunits
B)specific intrachain hydrogen bonds
C)salt links (ion-pair bonds)between ?-subunits
D)interchain salt bridges

Question 27

Which of the following is a function of the polypeptide of myoglobin?

A)protects the heme iron from oxygenation
B)keeps the heme iron in the ferric form
C)provides a pocket for iron to fit
D)cradles the heme group

Question 28

Which of the following is NOT a characteristic of hemoglobin's binding of oxygen?

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 deoxyHb.

Question 29

Which of the following is the reason why BPG shifts the oxygen saturation curve of Hb to the right?

A)BPG binds to deoxyHb and unloads O₂ at tissues.
B)BPG binds to oxyHb and unloads O₂ at tissues.
C)BPG binds to deoxyHb and unloads O₂ at the lungs.
D)BPG binds to oxyHb and unloads O₂ at the lungs.

Question 30

Which of the following mechanisms explains how carbon dioxide affects O₂ binding to Hb?

A)by directly binding to heme-Fe in the oxygen binding site
B)by forming iron carbonate with the heme-iron
C)by forming HCO₃-,which combines with H⁺ to increase CO₂ binding
D)by forming H⁺ + HCO₃-,where the H⁺ is an antagonist to oxygen binding to Hb

Question 31

Which of the following regarding the effect of protons on binding of O₂ by hemoglobin is NOT correct?

A)The saturation curve of Hb for O₂ is displaced to the left (greater binding)as acidity increases.
B)Actively metabolizing tissues produce acid,which is an antagonist of oxygen binding by Hb.
C)As pH decreases,dissociation of O₂ from Hb is enhanced.
D)The phenomenon is called the Bohr effect.

Question 32

Which of the following regarding the differences between Hb and Mb is NOT correct?

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)Hb-oxygen binding is dependent on physiological changes in pH,whereas Mb-oxygen binding is not.

Question 33

Why are we are protected to some extent against low level CO poisoning?

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.