9 TH W E E K
Gihan E-H Gawish, MSc, PhD
Ass. Professor
Molecular Genetics and Clinical
Biochemistry
KSU
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
After replication,
each DNA molecule=
one old strand and one
new strand.
Three possible models
Correct
Watson and Crick’s structure predicted that
base-pairing
would
guide
semi-conservative
replication.
Matthew Meselson and Franklin Stahl tested
this prediction by labeling DNA with 15N (heavy
isotope).
Animation
Animation
DNA Replication Fork
Click to Exam Yourself
Click to find the attached file
click to solve the quiz in this animation


3’OH of growing
chain
forms
covalent bond with
phosphate of dNTP.
DNA
polymerases
can
only
add
nucleotides to 3’
end
(5’—>3’
direction of synth.



1) Template to specify
complementary strand.
2) Primer (DNA or RNA)
bound to template by
base pairing. No DNA
pol. can start synth.
without a primer!!
3) dNTPs
DNA can be denatured and reannealed:
5’-GATCTTAGC-3’
3’-CTAGAATCG-5’
Heat to 95C
Cool to 70 C
5’-GATCTTAGC-3’
3’-CTAGAATCG-5’
When cooled, base-pairs find each
other and become double-stranded
(renature, reanneal, or hybridize).

Uses DNA replication to amplify tiny amounts
of DNA to give an amount large enough to be
analyzed.
Requires:




1)
2)
3)
4)
Small amount of template.
Specific primers that bind the template.
dNTPs.
A thermostable DNA polymerase.
Animation