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Molecular Biology: Lab Quiz II Answers
1. Which of the following statements is correct?
1. Longer DNA fragments migrate farther than shorter
fragments.
2. Migration distance is inversely proportional to the fragment
size.
3. Positively charged DNA migrates more rapidly than
negatively charged DNA.
4. Uncut DNA migrates farther than DNA cut with restriction
enzymes.
The correct answer is b. The smaller a fragment, the farther it will
migrate. This is an inverse relationship.
2. How many base pairs is the fragment circled in red below?
There are approximately 3500 base pairs in the circled fragment.
3. A teacher had her students perform this laboratory beginning with
setting up their own restriction enzyme digests. One team of
students had results that looked like those at left.
What is the most likely explanation for these results?
1. The students did not allow enough time for the
electrophoresis separation.
2. The agarose prepartion was faulty.
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3. The methylene blue did not stain the DNA evenly.
4. The DNA segment does not have a recognition sequence for
EcoRI.
5. The voltage was set too low on the apparatus.
The correct answer is d. If the restriction enzyme does not cut the
DNA, a single large fragment will remain.
Below is a plasmid with restriction sites for BamHI and EcoRI.
Several restriction digests were done using several combinations of
these two enzymes. Use the figure to answer questions 4–6.
Hint: Begin by determining the number and size of the fragments
produced with each enzyme.
4. Which lane shows a digest with BamHI only?
I
II
III
IV
The correct answer is III.
V
5. Which lane shows a digest with EcoRI only?
I
II
III
IV
V
The correct answer is II. With EcoRI alone, there will be a single cut
and only one fragment: 20kb.
6. Which lane shows the fragments produced when the plasmid was
incubated with both EcoRI and BamH1?
I
II
III
IV
V
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7. A restriction enzyme acts on the following DNA segment by
cutting both strands between adjacent thymine and cytosine
nucleotides
............TCGCGA.........
............AGCGCT.........
Which of the following pairs of sequences indicates the sticky ends
that are formed?
1.
2.
3.
4.
5.
...GCGC
...TCGC
...T
...GA
...GCGC
CGCG...
TCGC...
T...
GA...
GCGC...
The correct answer is a.
8. A segment of DNA has two restriction sites—I and II. When
incubated with restriction enzymes I and II, three fragments will be
formed—a, b, and c. Which of the following gels produced by
electrophoresis would represent the separation and identity of these
fragments?
The correct answer is b. The fragments, in decreasing order of size
are c, a, b.
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings