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.
electrophoresis separation.
2. The agarose prepartion was faulty.
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.
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.