DNA Replication
DNA Replication
DNA is replicated during the
“S” stage of the cell cycle.
DNA replication is necessary
for both Mitosis and
Meiosis.
Mitosis- growth, repair, and to
maintain surface to volume
ratio.
Meiosis- produce gametes
DNA Synthesis
Occurs in both Prokaryotes
and eukaryotes.
It take place in the nucleus
of eukaryotes.
It produces two identical
copies of DNA.
It is controlled by several
different enzymes;
helicase and DNA
polymerase
AT
GC
C G
T A
GC
AT
GC
C G
T A
GC
A T
GC
C G
T A
GC
Replication controlled by Enzymes
Helicase- unzips the hydrogen
bonds exposing the
nitrogen bases.
A replication fork is created (Y
shaped region).
New strands are produced at
the forks.
Replication – base pair rules
A - T
G - C
Synthesis
DNA polymerase adds
new nucleotides at the
replication fork.
New nucleotides can only
be added at the 3’ end
of the DNA.
5’
3’
Nucleotide
DNA Polymerase
RNA
Primer
5’
DNA Replication
Replication
Fork
DNA replication begin @ 1.42
Point of Origin
DNA Replication and Mutations
In humans, DNA replicates
approximately 50
nucleotides per second.
or
3,000 nucleotides per
minute
Base pair errors are made
during replication.
Mutation is a change in the
genetic code.
Preventing Mutations during
Replication
DNA polymerase makes about 1
in 10,000 errors.
Enzymes (DNA polymerase) act
as “Spell Checkers” correcting
the errors.
Proof reading results in only 1
error in 1 billion base pairs.
Semi- Conservative Model
Watson and Crick
recognized from their
model, that the DNA
could be easily copied.
The original strand is
opened and copied,
following base pair rules.
The resulting 2 identical
strands of DNA are
composed of both an
original (parental) and a
new copy.
1958- Meselson and Stahl
confirm the semiconservative model with an
experiment
Semi- Conservative Model
Each of the two new
strands of DNA are
composed of:
One original (parent)
strand
One new strand
Both are identical in every
way
DNA and Replication (13 min).