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CASE FILES: BIOCHEMISTRY
A N SW E R S TO C A SE 6: H E R P E S SIM P L E X V IR U S/
PO L Y M E R A SE C H A IN R E A C T IO N
Summary:
A 21-year-old female presents with recurrent episodes of painful
ulcerations on vulva. The physician uses a swab to sample the ulcer for diag-
nosis. She also has some neurologic symptoms at the vulva prior to appearance
of lesions.
Most likely diagnosis: Herpes simplex virus 2 (HSV-2) outbreak.
Biochemical Technique: Polymerase chain reaction to amplify the small
amount of HSV DNA. This is a very sensitive diagnostic technique that is
able to detect small amounts of HSV DNA, and through in vitro
techniques, it is able to rapidly produce large quantities of DNA.
C L IN IC A L C O R R E L A T IO N
This 21-year-old female has a recurrent episode of vulvar ulcers accompanied by
burning and tingling in the same region. These symptoms are caused by the her-
pes virus affecting the afferent nerve. After a primary infection, the herpes virus
lays dormant in the dorsal ganglia of the nerve root. Then in times of stress or
for unknown reasons, the virus becomes active and travels down the nerve to the
skin. Thus, the patient often has neurologic symptoms even before the outbreak
on the skin. Viral culture is an accurate method of diagnosis. Perhaps even bet-
ter is polymerase chain reaction (PCR), which can also be used for detection of
numerous infectious organisms, genetic mutations, and forensic testing.
A PPR O A C H TO PO L Y M E R A SE C H A IN R E A C T IO N
O bjectives
1.
Describe the life cycle of herpes simplex viruses.
2.
Describe the process of PCR.
3.
Know the definitions and purpose of restriction endonucleases and
oligonucleotides.
4.
Be familiar with how PCR may be used for identifying infections and
mutations.
5.
Cite the advantages of PCR over other biotechnology involving recombi-
nant DNA.
D efinitions
Annealing: The process of allowing single-stranded lengths of DNA to
base-pair to form double-stranded DNA. It is used most frequently when
referring to the process of binding an oligonucleotide primer or probe to
a longer DNA fragment.
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