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A
T
KEY:
CG
- Phosphate- Sugar- Adenine
- Thymine- Cytosine- Guanine
A T
C
C G
C G
T A
5’
5’3’
3’DNA at its natural state, would look like this. It is ready to replicate.
A T
C G
A T
C G
T A
A T
C G
A T
A T
C G
C G
C G
T A
T A
5’
5’3’
3’
This is DNA Helicase. As it starts to break apart the nitrogen bases the DNA’s walls begin to break apart.
A
T
KEY:
CG
- Phosphate- Sugar- Adenine
- Thymine- Cytosine- Guanine
A T
C
C
T
G
G
A
5’
5’3’
3’
A
T
KEY:
CG
- Phosphate- Sugar- Adenine
- Thymine- Cytosine- Guanine
A T
C G
A T
A
C G
T A
Helicase continues to pull apart the nitrogen bases.
A T
C
C
T
G
G
A
5’
5’3’
3’
A
T
KEY:
CG
- Phosphate- Sugar- Adenine
- Thymine- Cytosine- Guanine
A T
C G
A T
A
C G
T A
T
C
C
T
G
G
A
5’
5’3’
3’
A
T
KEY:
CG
- Phosphate- Sugar- Adenine
- Thymine- Cytosine- Guanine
A T
C G
A T
A
C G
T A
T
C
C
T
G
G
A
5’
5’3’
3’
A
T
KEY:
CG
- Phosphate- Sugar- Adenine
- Thymine- Cytosine- Guanine
A T
C G
A T
A
C G
T A
T
C
C
T
G
G
A
5’
5’3’
3’
A
T
KEY:
CG
- Phosphate- Sugar- Adenine
- Thymine- Cytosine- Guanine
A T
C G
A T
A
C G
T A
T
C
C
T
G
G
A
5’
5’3’
3’
A
T
KEY:
CG
- Phosphate- Sugar- Adenine
- Thymine- Cytosine- Guanine
A T
C G
A T
A
C G
T A
T
C
C
T
G
G
A
5’
5’3’
3’
A
T
KEY:
CG
- Phosphate- Sugar- Adenine
- Thymine- Cytosine- Guanine
A T
C G
A T
A
C G
T A
A
A
C
C
C
T
A
C
A
C
T
T
G
G
A
T
G
T
G
A
The leading and lagging strand start to “duplicate” in order to form two strands of DNA
A
C
C
C
T
A
C
A
C
T
T
G
G
A
T
G
T
G
A
C
A
C
A
C
T
The Okazaki fragments must be continued by DNA ligase.
A
C
C
C
T
A
C
A
C
T
T
G
G
A
T
G
A T
G
A
AA
C
A
C
A
C
T
C
C
TT
Once DNA ligase goes through the cycle the okazaki fragments are fixed by DNA ligase. As you can see there are no missing fragments in the lagging strand now.
A
C
C
C
T
A
C
A
C
T
T
G
G
A
T
G
A T
G
A
A
C
A
C
A
C
T
C
C
TT
T
G
T
G
A
A T
C
C
C
T
A T
C
A T
C
T
T
G
G
A
T
G
A T
G
A
A
C
A
C
A
C
T
C
C
TT
T
G
G
A
T
G
T
G
A
A T
C
C
C
T
A T
C
A T
C
T
T
G
G
A
T
G
A T
G
A
A
C
A
C
A
C
T
C
C
TT
T
G
G
A
T
G
T
G
A
DNA polymerase III goes through the nitrogen bases connecting them.
A T
C
C
C
T
A T
C
A T
C
T
T
G
G
A
T
G
A T
G
A
A
C
A
C
A
C
T
C
C
TT
T
G
G
A
T
G
T
G
A
DNA polymerase III goes through the nitrogen bases connecting them.
A T
C
C
C
T
A T
C
A T
C
T
T
G
G
A
T
G
A T
G
A
A
C
A
C
A
C
T
C
C
TT
T
G
G
A
T
G
T
G
A
DNA polymerase III goes through the nitrogen bases connecting them.
A T
C
C
C
T
A T
C
A T
C
T
T
G
G
A
T
G
A T
G
A
A
C
A
C
A
C
T
C
C
TT
T
G
G
A
T
G
T
G
A
DNA polymerase III goes through the nitrogen bases connecting them.
A T
C
C
C
T
A T
C
A T
C
T
T
G
G
A
T
G
A T
G
A
A
C
A
C
A
C
T
C
C
TT
T
G
G
A
T
G
T
G
A
DNA polymerase III goes through the nitrogen bases connecting them.
A T
C
C
C
T
A T
C
A T
C
T
T
G
G
A
T
G
A T
G
A
A
C
A
C
A
C
T
C
C
TT
T
G
G
A
T
G
T
G
A
DNA polymerase III goes through the nitrogen bases connecting them.
A T
C
C
C
T
A T
C
A T
C
T
T
G
G
A
T
G
A T
G
A
A
C
A
C
A
C
T
C
C
TT
T
G
G
A
T
G
T
G
A
DNA polymerase III goes through the nitrogen bases connecting them.
A
A T
C
C G
C G
T A
A T
C G
A T
C G
T A
A T
C
C G
C G
T A
A T
C G
A T
C G
T A
T
The DNA strands come together, then you have 2 complete DNA strands.
Purpose of all of this
The purpose of DNA replication is so that the genetic material can be passed of from the original cell to the “daughter” cell. This leads to the transfer of traits.
Problems
In 1953, biologists had noticed that most replication errors were caused by what are called Tautomeric shifts. These are the spontaneous isomerization (the conversion of a compound into an isomer of itself) of a nitrogen base to an alternative hydrogen-bonding form. Not only this can occur but also something called “strand slippage”. It involves denaturation and displacement of the DNA strands, resulting in mispairing of the complementary bases.
