Virginia Commonwealth University
BIOC 403 Exam 2 Key. Biochemistry 403 Exam #2
Multiple Choice (2 points each)
1. A 150 amino acid protein has ___________ potential amino acid sequences.
a. 150
b. 20150
c. 150
...
Virginia Commonwealth University
BIOC 403 Exam 2 Key. Biochemistry 403 Exam #2
Multiple Choice (2 points each)
1. A 150 amino acid protein has ___________ potential amino acid sequences.
a. 150
b. 20150
c. 15020
d. 150150
e. None of the above
2. Advantages of having a multisubunit protein include:
a. efficiency
b. Genetic economy in homo sapiens
c. Increased stability of subunits
d. All of the above
e. A and C
3. The most efficient enzyme inhibitor should resemble the:
a. substrate
b. product
c. transition state
d. solvation
e. none of the above
4. Urea denatures proteins by:
a. Increasing H bonds
b. Disrupting H bonds
c. Disrupting hydrophobic interactions
d. Increasing ionic interactions
e. Breaking covalent bonds
5. Energy stabilization of 3o structures comes mainly from:
a. Hydrophobic interactions
b. H bonds
c. ionic interactions
d. Covalent bonds
e. None of the above
6. Molecular Chaperones:
a. Form covalent bonds
b. Assist in protein folding
c. Increase 30 stability
d. Increase temperature
e. All of the above
7. Protein domains have:
a. Specific functions
b. Independent , stable structures
c. Predictable functional motifs
d. Structures stabilized by weak forces
e. All of the above
8. Enzyme interactions with substrate are best described by:
a. Lock and key
b. Rigid structure interactions
c. Induced fit
d. Ionic bonding
e. All of the above
9. What is the catalytic power of an enzyme if the rate of the catalyzed reaction is 1X105
molecules/sec and the uncatalyzed rate is 1X10-6 molecules/sec?
a. 1X1011
b. 1X10-11
c. 5X1010
d. 5X10-10
e. 8X102
10. All of the following are true for cofactors except:
a. They are usually tightly bound to protein
b. They are sometimes vitamins
c. Many are cations
d. They are non-protein components
e. None, all are true
11. For a Lineweaver-Burke plot:
a. X intercept= -1/Km
b. X intercept= Km/vmax
c. X intercept=-vmax
d. Y intercept=-vmax
e. None of the above
12. Conditions required for Michaelis-Menten kinetics include:
a. ES conversion to products is irreversible
b. Constant T and pH
c. 1 substrate reaction
d. [E]<<[S]
e. All of the above
13. The enzyme with the highest catalytic efficiency has:
a. kcat=2X10-2, Km=3X10-2
b. kcat=3X10-1, Km=5X102
c. kcat=4X104, Km=2X10-4
d. kcat=4X104, Km=1X10-8
e. cannot determine
14. The catalytically active complex of ___________ and _________ is called the
_______________.
a. apoenzyme; holoenzyme; cofactor
b. cofactor; holoenzyme; apoenzyme
c. holoenzyme; cofactor; apoenzyme
d. apoenzyme; cofactor; holoenzyme
e. none are true
15. 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.
16. Proteins generally fold in the following order:
a. Hydrophobic collapse, 2o structure interactions, 2o structure formation
b. 2o structure formation, 2o structure interaction, ionic collapse
c. 2o structure formation, 2o structure interaction, hydrophobic collapse
d. 2o structure interaction, ionic collapse, 3o structure interactions
e. None of the above
17. The first stage in protein folding is:
a. Formation of secondary structures
b. Interaction of secondary structures
c. Subunit binding
d. Hydrophobic collapse
e. None of the above
18. Molecular chaperones were first identified as:
a. Heat shock proteins
b. Secondary structures
c. Regulatory enzymes
d. Membrane proteins
e. None of the above
19. The active tertiary structure of an enzyme is usually:
a. Non-specific
b. Unfolded
c. The lowest energy conformation
d. The highest energy conformation
e. None of the above
20. The statement that all of the information needed for proper protein sequencing is contained in
the amino acid sequence is:
a. True for all proteins
b. False for all proteins
c. True for most proteins
d. True for fibrous proteins
21. (10 points) Why was ribonuclease A a good choice for Anfinsen’s experiment?
It contains 4 Cys-Cys disulifide bonds which are not denatured by urea.
22.
A. (10 points) Draw a double reciprocal plot representing competitive inhibition.
See text
B. (4 points)How does the inhibitor affect vmax and Km of the enzyme?
Increases Km, no effect on vmax
C. (2 points)Where on the enzyme does the inhibitor bind?
To active site
D. (4 points)To what forms of the enzyme does I bind?
I binds to Free e, not to ES complex
23. For an enzyme that follows Michaelis –Menten kinetics, k1=1X106 M-1 sec-1, k-1= 2x103
sec-1 and k2=2X 103 sec-1.
a. What is the Km for the enzyme ( 5 points)?
Km = k-1 + k2/k1 = .004M
b. If the enzyme concentration is 5 nanomoles in 1 ml, what is vmax for the enzyme (5
points)?
Vmax = [Et] k2 = 1 X 10-5 M/ml sec
c. What is the catalytic efficiency for this enzyme (5 points)?
Cat. Eff. = kcat/Km = k2/Km = 5 X 105 1/M sec
24. If [S] is 1/10 of Km, what is Vo in terms of vmax (10 points)?
Set S=1, Km=10 Vo=Vmax [S]/[S] + Km = Vmax (1)/(1) + (10)m = 1 Vmax/11
25. What is the function of a kinase (5 points)?
Kinases are enzymes that add phosphate groups to specific proteins at specific amino
acid residues to regulate protein activity.
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