qmorrisREMOVE at indiana.edu
Fri Nov 6 15:16:49 EST 1998
To increase yield? That's putting it mildly.
PCR is a technique by which tiny amounts of DNA are replicated over and
over so that there's lots of DNA. During each replication cycle, each strand of
the DNA molecule (there are two) separates from the other. Only when the
two strands are separated can replication take place.
And the only way to separate those strands is to heat them up. Really heat
them up -- to about 94 deg C. Once the strands are apart, a DNA
polymerase comes in and replicates each strand so that you end up with 2
double stranded, complete DNA molecules from the one double stranded
DNA molecule you started with.
Our DNA polymerase(s) works best around 98.6 deg F, or about
37 deg C. At 94 deg C, our DNA polymerase falls apart. It doesn't
work AT ALL.
You getting this? If we were to use our DNA polymerase for PCR,
the DNA would separate at 94 deg C but the polymerase would die,
and therefore PCR wouldn't work.
But DNA really only denatures above 50 deg C. So that was one of the
problems Kary Mullis solved when he suggested the use of a DNA
polymerase from another organism that lives at very high temperatures
(the bacterium Thermus Aquaticus or Taq for short), at about 94 - 95
This works really well! We need our DNA strands apart at 94 deg C
and we've got a DNA-making enzyme (DNA polymerase) that works
really well at 94 deg C.
> Gilbert Douglas wrote:
> > I have learned in my Sophomore biology class that one characteristic
> > significant to Thermophilic bacteria is the presence of a "Taq" enzyme. My
> > question is, what reaction does this enzyme catalyze in these bacteria and
> > why is this enzyme uniquely needed in the PCR?
> > I would appreciate any help
> > thanks,
> > gilbert douglas
> the Taq enzyme is a DNA polymerase. It is used in PCR because the
> polymerisation can proceed at higher temperatures than ordinary
> polymerases, and ceases to work at lower temperatures. The reactions are
> done through several heating-cooling cycles to increase yield and
> decreases errors.
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