CLINICAL CASES
63
B IO C H E M IS T R Y PE A R L S
Polymerase chain reaction (PCR) is an in vitro method for the expo-
nential amplification of a specific DNA region.
PCR involves (1) denaturation, which separates the two DNA chains
by heating the reaction mixture to 90°C to 95°C (194°F to 203°F);
(2) annealing or cooling to 45°C to 60°C (113°F to 140°F) so that
the oligonucleotide primers can bind or anneal to the separated
strands of the target DNA; and (3) elongation with DNA poly-
merase (at 72°C [162°F] when
Taq
DNA polymerase used)
adding nucleotides to the 3' ends of the primers to a complete
copy of the target DNA template.
GC pairs have three hydrogen bonds, whereas AT pairs have only
two hydrogen bonds and are therefore weaker.
A heat-stable DNA polymerase obtained from the thermophilic bac-
terium
T. aquaticus
is used to synthesize the new strands in most
PCR reactions.
Endonucleases usually act at sites of palindromes.
REFERENCES
Granner DK, Weil PA. Molecular genetics, recombinant DNA, & genomic technol-
ogy. In: Murray RK, Granner DK, Mayes PA, et al., eds. Harper’s Illustrated
Biochemistry, 26th ed. New York: Lange Medical Books/McGraw-Hill, 2003.
Johnson G, Nelson S, Petric M, et al. Comprehensive PCR-based assay for detec-
tion and species identification of human herpesviruses. J Clin Microbiol 2000;
38(9):3274-9.
previous page 77 Case Files   Biochemistry read online next page 79 Case Files   Biochemistry read online Home Toggle text on/off