HISTOTECHNOLOGY SOLUTION MANUAL
COMPREHENSIVE EXAM 2026 FULL
QUESTIONS AND ANSWERS
◉3. What normal role do restriction enzymes play in bacteria? How do
bacteria protect their own DNA from the action of restriction enzymes?
Answer: Solution:
Restriction enzymes cut foreign DNA, such as viral DNA, into
fragments. Bacteria protect their own DNA by modifying bases, usually
by methylation, at the recognition sites.
◉4. Explain how gel electrophoresis is used to separate DNA fragments
of different lengths. Answer: Solution:
Gel electrophoresis uses an electric field to drive DNA molecules
through a gel that acts as a molecular sieve. The gel is an aqueous matrix
of agarose or polyacrylamide. DNA molecules are loaded into a slot or
well at one end of the gel. When an electric field is applied, the
negatively charged DNA molecules migrate toward the positive
electrode. Shorter DNA molecules are less hindered by the agarose or
polyacrylamide matrix and migrate faster than longer DNA molecules,
which must wind their way around obstacles and through the pores in
the gel matrix.
◉5. After DNA fragments have been separated by gel electrophoresis,
how can they be visualized? Answer: Solution:
, DNA molecules can be visualized by staining with a fluorescent dye,
such as ethidium bromide, that intercalates between the stacked bases of
the DNA double helix, and the dye-DNA complex fluoresces when
irradiated with an ultraviolet light source. Alternatively, they can be
visualized by attaching radioactive or chemical labels to the DNA before
it is placed in the gel.
◉6. What is the purpose of Southern blotting? How is it carried out?
Answer: Solution:
Southern blotting is used to detect and visualize specific DNA fragments
that have a sequence complementary to a labeled DNA probe. DNA is
first cleaved into fragments with restriction endonucleases. The
fragments are separated by size via gel electrophoresis. These fragments
are then denatured and transferred by blotting onto the surface of a
membrane filter. The membrane filter now has single-stranded DNA
fragments bound to its surface, separated by size as in the gel. The filter
is then incubated with a solution containing a denatured, labeled probe
DNA. The probe DNA hybridizes to its complementary DNA on the
filter. After washing away excess unbound probes, the labeled probe
hybridized to the DNA on the filter can be detected using the appropriate
methods to visualize the label. For radioactively labeled probes, the
bound probe is detected by exposure to X-ray film. Other probe labeling
methods detect bound probe using enzymatic reactions that generate
luminescence or color.
◉7. Give three important characteristics of cloning vectors. Answer:
Solution:
Cloning vectors should have:
COMPREHENSIVE EXAM 2026 FULL
QUESTIONS AND ANSWERS
◉3. What normal role do restriction enzymes play in bacteria? How do
bacteria protect their own DNA from the action of restriction enzymes?
Answer: Solution:
Restriction enzymes cut foreign DNA, such as viral DNA, into
fragments. Bacteria protect their own DNA by modifying bases, usually
by methylation, at the recognition sites.
◉4. Explain how gel electrophoresis is used to separate DNA fragments
of different lengths. Answer: Solution:
Gel electrophoresis uses an electric field to drive DNA molecules
through a gel that acts as a molecular sieve. The gel is an aqueous matrix
of agarose or polyacrylamide. DNA molecules are loaded into a slot or
well at one end of the gel. When an electric field is applied, the
negatively charged DNA molecules migrate toward the positive
electrode. Shorter DNA molecules are less hindered by the agarose or
polyacrylamide matrix and migrate faster than longer DNA molecules,
which must wind their way around obstacles and through the pores in
the gel matrix.
◉5. After DNA fragments have been separated by gel electrophoresis,
how can they be visualized? Answer: Solution:
, DNA molecules can be visualized by staining with a fluorescent dye,
such as ethidium bromide, that intercalates between the stacked bases of
the DNA double helix, and the dye-DNA complex fluoresces when
irradiated with an ultraviolet light source. Alternatively, they can be
visualized by attaching radioactive or chemical labels to the DNA before
it is placed in the gel.
◉6. What is the purpose of Southern blotting? How is it carried out?
Answer: Solution:
Southern blotting is used to detect and visualize specific DNA fragments
that have a sequence complementary to a labeled DNA probe. DNA is
first cleaved into fragments with restriction endonucleases. The
fragments are separated by size via gel electrophoresis. These fragments
are then denatured and transferred by blotting onto the surface of a
membrane filter. The membrane filter now has single-stranded DNA
fragments bound to its surface, separated by size as in the gel. The filter
is then incubated with a solution containing a denatured, labeled probe
DNA. The probe DNA hybridizes to its complementary DNA on the
filter. After washing away excess unbound probes, the labeled probe
hybridized to the DNA on the filter can be detected using the appropriate
methods to visualize the label. For radioactively labeled probes, the
bound probe is detected by exposure to X-ray film. Other probe labeling
methods detect bound probe using enzymatic reactions that generate
luminescence or color.
◉7. Give three important characteristics of cloning vectors. Answer:
Solution:
Cloning vectors should have:
