DNA REPLICATION Flashcards
DNA SYNTHESIS =
DNA DUPLICATION=DNA REPLICATION
There are three ways that
DNA can be duplicated
- Conservative
- Semi-conservative
- Dispersive
Conservative
original is left completely original.
Semi-conservative
new DNA is half original and half new
Dispersive
DNA is randomly duplicated
Step 1 (Initiation) DNA helicases
unwinds & separates
the original DNA double helix.
- These proteins wedge themselves
between the two strands of the
double helix and
break the hydrogen
bonds between the base pairs
- As the double helix unwinds
the two complementary strands of DNA
separate from each other and form a Y shape.
Step 2 (Elongation): New DNA is
formed from DNA template.
RNA Primers attach
o specific regions (brought by DNA
primase).
New nucleotides are added to the primer by
the enzyme DNA Polymerase according to the base-pairing rules.
DNA polymerases
create the formation of the new
complimentary DNA molecule by moving along each strand in a 5’ to 3’ direction.
DNA polymerase add nucleotide
to a new daughter compliment in a 5’ to 3’
direction only
Step 2: Leading strand
Primers attach
Primers are?
Primers are pre-made sequences of RNA
Primers serve as tethers
from which replication can proceed from the 3’ end
DNA Polymerase attaches
free nucleotides to the 3’ end of the primer.
On the leading strand there is one primer
and the newly forming DNA follows the
replication fork as the new DNA is synthesized.
the LEADING STRAND
It has its new strand continuously synthesized as helicase unwinds more DNA.
the LAGGING STRAND
is discontinuous replication because it the bases are oriented in the wrong direction
The lagging strand creates
a particular problem for replication
Multiple primers attach to the lagging strand as the replication fork moves forward
creating what are known as “Okazaki
Fragments”
A special enzyme, call ligase
joins Okasaki fragments
together to form one continuous molecule
The process completes when
all the original bases have been paired with a new complementary nucleotide
Each double-stranded DNA helix is now
made of one new strand of DNA and one
original strand of DNA
