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Outcomes
DNA Replication
3.4.1 Explain DNA replication in terms of
unwinding the double helix and separation of
the strands by helicase, followed by
formation of the new complementary
strands by DNA polymerase.
3.4.2 Explain the significance of
complementary base pairing in the
conservation of the base sequence of DNA.
3.4.3 State that DNA replication is semiconservative.
IB Biology Core Topic 3.4
DNA Replication
replication is a process that copies
a strand of DNA to produce a new
strand with the same sequence of bases.
When a cell is preparing to divide it must
copy all of the DNA in
effect doubling the
amount of DNA
found in the cell.
When DNA is getting ready to replicate it is in the
form of chromatin and not the highly condensed
chromosomes.
Two things are needed for DNA replication;
enzymes which include DNA helicase and a group
of enzymes called DNA polymerase and free
floating nucleotides.
The first step in the replication of DNA involves
the unwinding of the parent strand. Once the
double helix unwinds the two strands need to
separate.
DNA
The
hydrogen bonds between the
complementary base pairs need to be
broken in order to separate the DNA
strands.
The enzyme DNA helicase is used to break
the hydrogen bonds and unzip the DNA
strand.
The unzipped strands of DNA now act as
templates to build the new complementary
strands.
Free floating nucleotides that are found inside
the nucleus form complementary hydrogen
bonds with the nucleotides in both of the
DNA parent strands.
The nucleotides are also forming covalent
bonds as the sugar and phosphate backbone of
one side of the DNA is forming.
This forms two new strands of DNA
The enzyme DNA polymerase is responsible
for attaching the free floating nucleotides to
the parent strands to form the replicated
DNA.
The result is two
identical strands of
DNA, each
containing half of
the original parent
strand and they
will wind back into
double helices
Complimentary Base Paring
The complementary base pairing ensures
that each of the new strands is
complementary to the template used to
make it which ensures exact copying and the
base sequence of DNA nucleotides is
conserved.
Due to the fact that each nitrogen base will
only fit with one other base, it ensures that
the two new daughter strands are identical
to each other and the parent strand from
which they were made.
SemiSemi-Conservative Replication
DNA replication is a process that copies a
strand of DNA to produce a new strand
with the same sequence of bases.
DNA replication is semi-conservative
because each new strand produced by
replication contains half of the original
parent strand.
In other words, half the parent strand is
conserved in each of the new daughter
strands.
An Animation (only the first two
parts for SL!)
http://www.youtube.com/watch?v=oNW_
ykH3AvA&feature=related