exam 2

Question 1

What statements correctly describe hemoglobin?
i) Hemoglobin has globular structure composed two α- (141 amino acids) and two β-polypeptide chains
ii) Iron oxidation state changes from Fe2+ in T state to Fe3+ in R state.
iii) Hemoglobin contains a heme group, which is a protoporphyrin ring with an Fe2+ atom in its center
iv) Fe2+ of Hb can bind carbon monoxide
v) Oxygen affinity to hemoglobin can be allosterically altered by BPG.
vi) Each subunit of hemoglobin is myoglobin-like, containing 6 α-helical segments denoted A-H with connecting segments named AB, BC, CD, etc based on the helices they join
a) i, iii, iv, v
b) i, iv, v
c) ii, iv
d) iii, iv, v
e) i, iv

Answer 1

a) i, iii, iv, v

Question 2

Hemoglobin can interact with several molecules including H2S, CO and O2. Which statement(s) is(are) incorrectly describe such interactions?
i) Oxidization of the Fe(II) to Fe(III) prevents binding of O2; Fe(III) – heme complex is colored brown.
ii) Binding of O2 by Fe(II) –heme complex alters the electronic state of the complex changing the color from scarlet to dark purple.
iii) Affinity of CO is lower than the affinity of O2
iv) Affinity of O2 can be altered by CO2 and BPG
v) Hb interaction with CO2 results in an increase in pH.
a) i and iv
b) i, ii, iv
c) ii, iii, v
d) v
e) ii, v

Answer 2

c) ii, iii, v

Question 3

What are the fundamental differences between the saturation fraction (Y) and dissociation constant (Kd) that describe the interaction of Mb with oxygen?
i) Kd describes the interactions between oxygen and only one molecule of Mb, while Y represents the fraction of Mb molecules loaded with oxygen.
ii) Y describes the interactions between oxygen and only one molecule of Mb, while Kd represents the fraction of Mb molecules loaded with oxygen Because Kd is only a dissociation constant.
iii) Y and Kd describe the same things.
iv) Kd=[(Mb)*pO2]/(MbO2), while Y=(MbO2)/Mb+MbO2.
v) Kd=(MbO2)/(Mb) *pO2, while Y=(MbO2)/Mb+MbO2.
vi) Kd=[(Mb) + pO2]/(MbO2), while Y=(MbO2)/Mb * MbO2.
a) ii, iv
b) ii, v
c) ii, vi
d) i, iv
e) iii, iv

Answer 3

d) i, iv

Question 4

What factors contribute to the S-shape curve of Hb?
i) Cooperativity of all four subunits of Hb
ii) Multi-subunit nature of Hb
iii) localization of Hb in red blood cells
iv) interactions between Hb and Mb
v) Borr effect
vi) Conformational (T to R) shift
a) i, ii, vi
b) i, ii
c) i, ii, v
d) iv, v, vi
e) i, ii, iv

Answer 4

a) i, ii, vi

Question 5

Which of the following events does not take place upon O2 binding?
i) Fe pulls into the heme plane; F helix moves.
ii) There is a 15-degree shift in tertiary structure
iii) There are sliding contacts between Asp G1 (99) of a1 and Tyr C7 (42) of b2
iv) There is a 15-degree shift between T and R states
v) Fe pulls into the heme plane; B helix moves.
a) i, iv
b) i, ii, iii
c) i, v
d) ii, iii, v
e) i, ii, iv

Answer 5

d) ii, iii, v

Question 6

If only 100 molecules of Hb and 100 molecules of Mb were present in the body, based on the graph shown above, how many molecules of Hb and Mb would be loaded with oxygen in resting and working muscles?
a) In resting muscles, 100 Mb and 80 Hb; in working muscles, 80 Mb and 10 Hb
b) In resting muscles, 80 Mb and 100 Hb, in working muscles, 80 Mb and 10 Hb.
c) In resting muscles, 80 Mb and 100 Hb, in working muscles, 10 Mb and 80 Hb
d) In resting muscles, 80 Mb and 10 Hb, in working muscles, 100 Mb and 80 Hb.
e) None of the above.

Answer 6

a) In resting muscles, 100 Mb and 80 Hb; in working muscles, 80 Mb and 10 Hb

Question 7

What physical and chemical factors alter O2 binding to Hb?
i) Interaction of CO2 with N termini of the protein.
ii) Activity of carbonic anhydrase
iii) pH in muscles and lungs
iv) BPG binding to Hb
v) Concentration of O2.
vi) Concentration of CO2.
a) ii, iii, iv, v
b) ii, iii, v, vi,
c) i, ii, iii, iv, v, vi.
d) i, v, vi
e) i, ii, iv, v

Answer 7

c) i, ii, iii, iv, v, vi.

Question 8

What statement(s) is incorrect about Hb as a CO2 transporter?
i) While some CO2 transported as HCO3– is carried in the blood, some CO2 binds to the N-terminal amino groups of the Hb subunits to form carbamates
ii) CO2 exclusively binds to the heme of Hb
iii) Binding of CO2 decreases the Bohr effect by removing H+ from the cell media
iv) Hb is responsible for all CO2 transported by the blood to be expelled in the lungs
v) Hb cannot transport CO2; it only can transport O2.
a) ii, iii, iv, v
b) i, v
c) i
d) v
e) ii, v

Answer 8

a) ii, iii, iv, v

Question 9

What is Polycythemia?
a) a site mutation in a or b subunit (methemoglobin subunit) leads to oxidation of Fe2+ (Fe3+) and reduces O2 binding cooperativity
b) a mutation in Hb that increase Hb’s O2 affinity, results in increased red blood cells to compensate for less O2 being delivered leading to a ruddy complexion
c) a disease that is characterized by mis-shaped red blood cells that cannot pass through capillaries properly
d) deficiency in red blood cells, compromises O2 delivery to tissues
e) a condition that is described by irreversible CO binding to Hb

Answer 9

b) a mutation in Hb that increase Hb’s O2 affinity, results in increased red blood cells to compensate for less O2 being delivered leading to a ruddy complexion

Question 10

Enzymes that transfer chemical groups to form one substrate to another are called:
a) Oxidoreductases
b) Lyases
c) Isomerases
d) Ligases
e) Transferases

Answer 10

e) Transferases

Question 11

The main function of ligases is to:
a) Transfer of functional groups
b) Oxidation-reduction (Redox) reactions
c) Hydrolysis
d) Break various chemical bonds by means other than hydrolysis and oxidation, often forming a new double bond
e) Link two molecules by forming a new chemical bond

Answer 11

e) Link two molecules by forming a new chemical bond

Question 12

What statement is correct about substrate specificity of enzymes?
a) Nearly all enzymes that participate in chiral reactions are absolutely stereospecific
b) Most enzymes catalyze reactions of a broad range of compound
c) Substrate specificity is not observed for oxidoreductases
d) Substrate specificity is a unique feature of isomerases
e) All of the above

Answer 12

a) Nearly all enzymes that participate in chiral reactions are absolutely stereospecific

Question 13

Select all species that can be prosthetic groups:
i) Mn2+
ii) NAD+
iii) ATP
iv) Zn2+
v) Hb
a) ii and iii
b) i and iv
c) i
d) ii
e) iii

Answer 13

b) i and iv

Question 14

Based on the graph shown above, calculate Km, kcat and specificity constant.
a) Km=0.1; kcat=0.005; specificity constant=0.1
b) Km=0.05; kcat=0.0025; specificity constant=0.5
c) Km=0.05; kcat=0.005; specificity constant=0.1
d) Km=0.05; kcat=0.0025; specificity constant=0.05
e) Km=0.5; kcat=0.025; specificity constant=0.5

Answer 14

c) Km=0.05; kcat=0.005; specificity constant=0.1

Question 15

If [S]= 10 mM , Km= 0.001 mM and Vmax is 50 mM/s. What is V0 for this enzymatic reaction?
a. V=100 M/s
b. V=20 mM/s
c. V=50 mM/s
d. V= 50 mM/s
e. V=20 μM/s

Answer 15

c. V=50 mM/s

Question 16

Compounds A and B were added to the catalytic reaction. Blue curve represents the compound A and red curve represents the compound B. What conclusions can be made from this experiment?
i. Compounds A and B are irreversible inhibitors
ii. Compounds A and B do not change the rate of the reaction
iii. Compounds A and B are competitive inhibitors
iv. Compound A exhibits stronger inhibition than compound B.
v. Compound B exhibits stronger inhibition than compound A.
a. ii, v b. i, iv c. iii, iv d. i, v e. i, iii, v

Answer 16

c. iii, iv

Question 17

What is Ki for compound A if the concentration of the inhibitor is 30 mM?
a) 13
b) 10
c) 1
d) 0.5
e) 100

Answer 17

b) 10

Question 18

18. Calculate Ki’ and α’ for the inhibitor that altered rates of enzymatic reaction according to the graph shown above.
    a) Ki’=20; α’=1.5
    b) Ki’=2; α’=6
    c) Ki’=2; α’=1
    d) Ki’=20; α’=2
    e) Ki’=20; α’=1

Answer 18

a) Ki’=20; α’=1.5

Question 19

19. Based on the free energy profiles of two catalysts, what catalysts is the most efficient?
    a) A
    b) B

Answer 19

b) B

Question 20

20. What is the ΔΔG‡ of the reaction catalyzed by catalyst A?
    a) 30
    b) 20
    c) 10
    d) 50
    e) 0

Answer 20

b) 20

Question 21

21. Conformational distortions accompanying formation of tetrahedral intermediates (structures 2 and 3) cause the carbonyl oxygen to move deeper into active site: oxyanion hole. Which statements are true about oxyanion hole?
    a. Serve to lower the transition state free energy for the formation of the tetrahedral intermediate
    b. Decelerate catalytic rate of enzymes
    c. Are responsible for a change in optimal pH of the enzyme
    d. Located in the active site of the enzyme
    e. A and D

Answer 21

e. A and D

Question 22

22. Place the following structures in the order in which they are formed in the chymotrypsin mechanism
    A. 1,2, 3
    B. 2, 3, 1
    C. 3, 2, 1
    D. 3, 1, 2
    E. 2, 1, 3

Answer 22

D. 3, 1, 2

Question 23

23. Which of the following statements concerning metal ion cofactors are true?
    a. Bind to substrates for orientation
    b. Mediate RedOx reactions by changing oxidation state
    c. Stabilize negative charges
    d. All of above
    e. None of above

Answer 23

d. All of above

Question 24

What statements are correct for uncompetitive inhibition:
i. inhibitor binds to the enzyme substrate complex
ii. inhibitor binds to the free enzyme
iii. Vmax is increased
iv. Vmax and Km change proportionally
v. only Km change
a. i, iii, iv
b. ii, iii, v
c. ii, iii, iv
d. i, iv
e. i, v

Answer 24

d. i, iv

Question 25

25. What type of inhibition is illustrated in the Figure 3, if His 57 located in the active site of chymotrypsin? f. Competitive g. Uncompetitive h. Mixed i. Irreversible j. Noncompetitive

Answer 25

i. Irreversible

Question 26

26. What statements are false about carbonic anhydrase? i. It requires Zn ion as a cofactor. ii. Zn ion coordinates OH- that acts as a nucleophile iii. nucleophilic attack causes scissoring of the peptide bond iv. this enzyme has aspartic amino acid residues coordinated to Zn v. activity of carbonic anhydrase decreases pH a. iii, v b. i, ii, v c. iii, iv d. ii, v e. ii, iv

Answer 26

c. iii, iv

Question 27

27. For the reaction A+B -> C, the reaction rate is expressed by v=k[A]. What statement is correct about this rate interpretation of the reaction: a) This is highly likely a psuedo-first-order reaction, where [B] >>> [A] b) This is highly likely a psuedo-first-order reaction, where [A] >>> [B] c) For this reaction, the rate has to be expressed only as v=k[A]2. d) In this reaction, the concentration of B will increase overtime. e) Kinetic order of this reaction cannot be determined.

Answer 27

a) This is highly likely a psuedo-first-order reaction, where [B] >>> [A]

Question 28

28. Based on the information provided in the table 12-1, what substrate, CO2 or HCO3- does have greater affinity to carbonic anhydrase? a) CO2 because it has greater Kcat b) HCO3- because it has lower Kcat/Km c) CO2 because it has lower Km d) HCO3- because it has greater Km e) CO2 because the net sum of all constants is lower.

Answer 28

c) CO2 because it has lower Km

Question 29

29. Why Vmax is only the theoretical maximal rate of the reaction that cannot be reached in reality (in the experiment)? a) It is nearly impossible to have all molecules of the enzyme interact with the molecules of substrate b) Because for the first order reactions, V0 is equal to ½ Vmax c) Because k2 is always greater than k1 d) Because k1 is always greater than k-1 e) Because Km is always greater than Kcat

Answer 29

a) It is nearly impossible to have all molecules of the enzyme interact with the molecules of substrate

Question 30

30. ATCase’s activity can be altered by ATP and CTP. What is true about CTP and ATP for this enzyme? a) CTP is an allosteric inhibitor; ATP is an allosteric activator b) ATP is an allosteric inhibitor; CTP is an allosteric activator c) CTP irreversibly inhibits ATCase d) Both ATP and CTP are allosteric inhibitors. e) Both ATP and CTP are allosteric activators.

Answer 30

a) CTP is an allosteric inhibitor; ATP is an allosteric activator

Question 31

31. What statement correctly describes covalent modification of enzymes? a) Covalent modifications are reversible b) Phosphorylation is a covalent modification of enzymes c) Covalent modification is used to alter enzyme activity d) All of the above e) None of the above

Answer 31

d) All of the above

Question 32

32. Based on the observed pH profile, which of the following is NOT a conclusion you would make from the data shown? a. This is an alkaline protease, having increased activity at more basic pH b. This pH profile is bell shaped c. The optimal catalytic activity is due to the protonation of one critical residue and deprotonation of another critical residue d. This enzyme likely has an active site glutamate residue that is involved in acid/base catalysis for enzymatic activity e. The pH optimum for this enzyme is pH 5

Answer 32

a. This is an alkaline protease, having increased activity at more basic pH

Question 33

33. Consider the function of insulin in response to high blood glucose levels. Which of the following most accurately describes the regulation of insulin. a. Proteolysis of proinsulin by trypsin allows for activation of insulin b. Proteolysis is used to activate proinsulin so the inactive precursor can be made earlier and only activated when needed c. Insulin expression only occurs in the presence of high blood glucose d. Proinsulin is covalently modified by insulin kinase for activation e. ATP binds to proinsulin to make it active, signaling high energy status of the body

Answer 33

b. Proteolysis is used to activate proinsulin so the inactive precursor can be made earlier and only activated when needed

Question 34

34. What is true about fetal Hb? i. Fetal Hb has low affinity to BPG ii. Fetal Hb is α2γ2 iii. It is composed of 5 subunits to enable more efficient O2 transport iv. Fetal Hb is smaller than normal Hb because fetus body is small a. i and ii b. i and iii c. i, iii and iv d. i e. i and iv

Answer 34

a. i and ii