BIOCHEMISTRY 410
Section 503
EXAM 3A
April 25 2001
Name____________________
I.D. _____________________
19. Enzyme A and enzyme B both catalyze the same reaction with the same substrate. In terms of product formed in a unit
of time, Enzyme A is 1.2 times faster than enzyme B. Which enzyme has the lower Km?
a) Enzyme A
c) neither
e) cannot tell on the basis of the data given
b) Enzyme B
d) both have the same
20. Chymotrypsin is an example of what type of enzyme? [p286]
a) kinase
b) transferase
c) oxido-reductase
d) hydrolase
e) isomerase
21. What type of enzyme requires pyridoxal phosphate, derived from vitamin B6: [p287]
a) kinase
b) transferase
c) oxido-reductase
d) hydrolase
e) isomerase
22. Enzymes in the blood coagulation cascade are predominantly: [p318]
a) proteases
b) dehydrogenases
c) nucleases
e) carboxylases
d) synthetases
23. An extract from liver and an extract from muscle were both tested with the same substrate. The reaction catalyzed by
the liver enzyme gave twice the free energy yield as the muscle enzyme. This must mean that:
a) twice as much substrate was used in the reaction with the liver enzyme
b) twice more liver enzyme was in the extract
c) the liver enzyme was two-times faster than the muscle enzyme
d) the liver enzyme had a lower Km than the muscle enzyme
e) the enzyme in the liver and muscle were not the same enzyme
24. The nerve poisons sarin, malathion, and parathion all target which enzyme in a living system: [p308]
a) chymotrypsin
c) acetylcholinesterase
e) none of those named
b) alcohol dehydrogenase
d) carboxypeptidase
25. Besides serine, what other amino acid residue would be expected to be at the active site of a serine protease? [p308]
a) glycine
b) alanine
c) histidine
d) proline
e) threonine
26. At very low substrate concentration the rate of an enzyme catalyzed reaction:
a) is first order with respect to [S]
d) is zero order with respect to [S]
b) is linear with time
e) a or c
c) is dependent only on concentration of free enzyme
27. An enzyme has a Km of 3.3 micromolar. At what [S] will that enzyme be half-saturated with S?
a) 3.3 micromolar
b) 1.5 micromolar
c) at half Vmax
d) 33 micromolar
28. An inhibitor that is capable of raising the Km of an enzyme for its substrate would be expected to:
a) resemble the structural features of the substrate
b) bind at a site other than the substrate site on the enzyme
c) form a complex with [ES]
d) decrease the slope of a Lineweaver-Burk plot
e) inactivate the enzyme
29. As compared to a competitive inhibitor, only a mixed inhibitor will:
a) bind to the surface of the enzyme
d) intercept the same point on the y axis
b) raise the slope of a Lineweaver-Burk plot
e) all of the above
c) lower the Vmax of the reaction
O
CH3
HN
vo =
Vmax[S]
Km( 1+ I ) + [S]
Ki
O
HOCH2
N
O
- +
N= N= N H
H
e) b or c
30. The equation on the left is used to calculate the Ki of : [p338]
a) a competitive inhibitor
c) either a mixed or competitive inhibitor
b) a mixed inhibitor
d) an uncompetitive inhibitor
e) an allosteric enzyme
31. The compound shown on the right above (3-azido-3’-deoxythymidine) is an effective inhibitor of: [p336]
a) nucleases
c) reverse transcriptase
e) succinate dehydrogenase
b) serine proteases
d) bisubstrate enzymes
32. Another name for 3-azido-3’-deoxythymidine is: [p336]
a) Ritonavir
c) didanosine
b) Nevirapine
d) aspirin
e) AZT
PROBLEMS: (20 points)
(8 pts) A liver enzyme at Vmax catalyzed the change of 250 micromoles of substrate in one minute. When [S] was 25
micromolar, the velocity was 100 micromoles per minute. In the presence of 25 micromolar inhibitor the observed velocity
was 80 micromoles per minute with 25 micromolar substrate present, and 250 micromoles per minute with a large excess of
substrate. Calculate the Km of the enzyme and the Ki of the inhibitor?
(4 pts) Draw and name the structure of the substrate for the enzyme “maltase”.
(4 pts) Draw and name any fatty acid with more than 16 carbons with a melting point lower than oleic acid
(4 pts) Draw and name your favorite steroid.
Questions 1-30 are 2.5 points each (use scantron). One correct answer. [brackets indicate page in textbook with answer]
1.
2.
The sugar in DNA has a deoxy group on carbon number:
a) 2
b) 1
c) 5
d) 3
e) 3 or 5
The sugar in RNA has a deoxy group on:
a) 1
b) 2
c) 3
e) none of the carbons
d) 4
3.
What is the approximate base tilt normal to the helix axis in the B form of DNA: [p728]
a) >28o
b) 10-15o
c) 18-25o
d) 25-28o
e) <10o
4.
If adenine pairs with thymine in A DNA, what does it pair up with in the B form of DNA?
a) guanine b) uracil
c) thymine
d) a second adenine
e) it has no paired base in the B form
5.
No change in A260 when a polynucleotide is heated means the polynucleotide in the solution is probably:
a) duplex DNA
b) a DNA-RNA hybrid
c) single stranded RNA or DNA
d) a double stranded RNA
e) c and d
6.
As a heated solution of DNA slowly cools down, the A260 absorbance reading will: [p740]
a) remain steady
`
c) decrease slightly
e) be lost completely
b) increase slightly
d) return to the starting absorbance
7.
When DNA is supercoiled, the molecule tends to be more:
a) linear
b) compact
c) circular
8.
9.
d) unwound
e) self-replicating
A DNA molecule has a linking number of 10. Spot the topoisomers of this molecule:
a) T = 11, W = 1 b) T = 12, W = 2
c) T = 9, W = +1
d) T = 13, W = 3
Which of the following is a DNA molecule existing in a relaxed state?
a) L = 10, T = 11, W = 1
c) L = 9, T = 10, W = 1
b) L = 9, T = 8, W = +1
d) L = 10, T = 10, W = 0
CH3
4
N
O:
3N
H
H
HN
e) all are
e) all are in a relaxed state
N
N
6
:N 1
N
O
10. Illustrated above is base pairing between:
a) adenine and thymine
c) adenine and uracil
b) guanine and cytosine
d) cytosine and adenine
e) adenine and guanine
11. A researcher who applies the technique of Western blotting is interested in detecting:
a) DNA
b) RNA
c) circular DNA
d) DNA-RNA hybrids
e) proteins
3’-ATTCTGACGTTAGGCAC-5’
CTGCAATC
12. Predict the next base to be incorporated by a DNA polymerase into the duplex DNA strand shown above:
a) A
b) T
c) C
d) G
e) a or c
13. Theta structures () and theta replication is another way of referring to:
a) circular DNA
c) DNA-RNA hybrids
b) DNA with replicating forks
d) a stem loop structure
14. Which polymerase enzyme shows the highest processivity?
a) DNA polymerase II
c) DNA polymerase I
b) DNA polymerase III
d) RNA polymerase
e) a transcription bubble
e) all have about the same
Questions 19-26: REFER TO THE DOUBLE STRANDED DNA STRUCTURE BELOW:
TOP STRAND……….. A T T C G A T G G C A G A U G T A
BOTTOM STRAND 5’- T A A G C T A C C G T C T A C A T -3’
Answer A = TOP, B = BOTTOM, C = BOTH,
15.
16.
17.
18.
Replication or Transcription
D = NEITHER
Which strand during replication becomes the leading strand: ABCD
Which strand is replicated by extending an RNA primer: ABCD
Which strand is also a template for DNA polymerase I: ABCD
Which strand when replicated is NOT proof read during synthesis: ABCD
19. Which enzyme during catalysis transfers a phosphate group derived from either NAD + or ATP to the substrate:
a) DNA gyrase
c) RNA polymerase II
e) DNA ligase
b) Topoisomerase II
d) alcohol kinase
20. Which enzyme uses RNA as a template to synthesize DNA:
a) reverse transcriptase
c) DNA transcriptase
b) telomerase
d) RNA transcriptase
e) a and b
21. In the bacterial cell, LexA and RecA become activated when DNA is
a) translated
c) transcribed
e) b and c
b) synthesized
d) damaged
4. What is an Okazaki fragment? What does it signify?
(5pt Maximum) CHOOSE WISELY
1. List all of the enzymes required for DNA synthesis on the lagging strand during normal replication: One point for a
correct answers, one point subtracted for any incorrect answer
5 pt BONUS
A biochemist was studying DNA replication. He (she) used single stranded DNA as a template and a cell extract as a
source of polymerase enzymes and binding proteins. All of the conditions found in the cell were faithfully duplicated in the
in vitro system. -labeled 32P-ATP along with CTP, GTP, TTP was added to start the reaction. After 15 minutes a test of
the reaction mixture revealed no radioactivity in the polymerized product. Moreover, the product that was made could not
be digested with DNase. Two errors were committed. You’ll earn one point if you spot one error and 5 points if you spot
both errors.
Gamma-labeled 32P nucleotides and ribonucleotides instead of deoxyribonucleotides.