The document depicts the process of DNA replication through a series of diagrams: 1) DNA helicase unwinds and separates the double helix into two single strands. 2) The leading and lagging strands begin to duplicate, with the lagging strand forming Okazaki fragments. 3) DNA ligase joins the Okazaki fragments on the lagging strand. 4) DNA polymerase III adds complementary nucleotides to each single strand, reforming the double helix structure and producing two identical DNA molecules.

1. 5’
T
A
C
A
A
DNA at its natural state,
would look like this. It is
ready to replicate.
G
T
A
T
C
C
3’
G
KEY:
- Phosphate
T
- Sugar
C
G
C
G
A
G
5’
3’
T
- Adenine
- Guanine
C T
A
Cytosine
- Thymine

2. 5’
C
A
G
C
This is DNA Helicase. As it
starts to break apart the
nitrogen bases the DNA’s
walls begin to break apart.
T
A
T
A
3’
T
A
G
KEY:
- Phosphate
T
- Sugar
C
G
A
3’
C
G
5’
- Adenine
G
- Guanine
C -
T
A
T
Cytosine
- Thymine

3. 5’
T
A
C
A
A
Helicase continues to pull apart
the nitrogen bases.
G
T
A
T
C
3’
G
KEY:
- Phosphate
T
- Sugar
C
3’
C
G
A
G
5’
- Adenine
G
- Guanine
C -
T
A
T
Cytosine
- Thymine

4. 5’
A
T
C
G
A
T
A
T
C
A
3’
G
KEY:
- Phosphate
T
- Sugar
C
3’
C
G
A
G
5’
- Adenine
G
- Guanine
C -
T
A
T
Cytosine
- Thymine

5. 5’
A
T
C
G
T
A
A
T
C
A
3’
G
KEY:
- Phosphate
T
- Sugar
C
3’
C
G
A
G
5’
- Adenine
G
- Guanine
C -
T
A
T
Cytosine
- Thymine

6. A
T
C
G
5’
T
A
A
T
C
A
3’
G
KEY:
- Phosphate
T
- Sugar
C
3’
C
G
A
G
5’
- Adenine
G
- Guanine
C -
T
A
T
Cytosine
- Thymine

7. 5’
A
T
C
G
T
A
A
T
C
A
3’
G
KEY:
- Phosphate
T
- Sugar
C
3’
C
G
A
G
5’
- Adenine
G
- Guanine
C -
T
A
T
Cytosine
- Thymine

8. 5’
A
T
C
G
T
A
A
T
C
A
3’
G
KEY:
- Phosphate
T
- Sugar
C
3’
C
G
A
G
5’
- Adenine
G
- Guanine
C -
T
A
T
Cytosine
- Thymine

9. A
C
3’
T
G
5’
T
A
A
T
C
A
G
KEY:
- Phosphate
T
- Sugar
C
3’
C
G
A
G
5’
- Adenine
G
- Guanine
C -
T
A
T
Cytosine
- Thymine

10. T
A
C
A
G
T
A
T
C
C
The leading and
lagging strand start to
“duplicate” in order to
form two strands of
DNA
G
T
A
C
G
C
G
T
A
A

11. T
A
G
C
T
A
A
T
G
C
C
A
T
A
C
G
C
A
G
C
T
T
The Okazaki
fragments must be
continued by DNA
ligase.
A

12. T
A
A
A
G
C
C
A
A
T
C
C
A
T
C
C
T
G
A
T
A
A
C
C
G
C
C
G
T
T
T
A
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.

13. T
A
A
G
C
C
A
A
A
T
C
C
A
T
C
C
T
G
T
T
A
A
G
C
G
C
C
G
T
T
A
T
C
A
T

14. TT
A
C
A
C
C
TT
A
A
T
A
T
A
G
TT
A
G
C
G
T
T
A
C
C
G
T
A
C
G
C
G
C
G
C
G
T
A
T
T
A

15. TT
A
C
A
G
A
A
G
G
C
C
A
G
T
A
C
G
C
G
C
G
C
G
A
T
T
A
T
DNA polymerase III
goes through the
nitrogen bases
connecting them.
T
T
A
TT
A
C
TT
T
C
C
T
A

16. TT
A
C
A
G
AA
T
A
G
TT
A
C
TT
T
C
C
T
A
C
C
G
DNA polymerase III
goes through the
nitrogen bases
connecting them.
T
A
G
T
A
C
G
C
G
C
G
C
G
A
T
T
A
T

17. TT
A
C
A
G
AA
G
DNA polymerase III
goes through the
nitrogen bases
connecting them.
T
A
T
A
C
C
G
TT
A
C
TT
T
C
C
T
A
G
T
A
C
G
C
C
G
C
G
A
T
T
A
T
G

18. TT
A
C
A
G
AA
G
DNA polymerase III
goes through the
nitrogen bases
connecting them.
T
A
T
A
C
C
G
TT
A
C
TT
T
C
C
T
A
G
T
A
C
G
C
G
C
G
C
G
A
T
T
T
A

19. TT
A
C
A
G
C
C
AA
G
DNA polymerase III
goes through the
nitrogen bases
connecting them.
T
A
T
A
G
TT
A
C
TT
T
T
A
C
C
G
T
A
C
G
C
G
C
G
C
G
A
T
T
A
T

20. TT
A
C
A
G
C
C
AA
G
DNA polymerase III
goes through the
nitrogen bases
connecting them.
T
A
T
A
G
TT
A
C
TT
T
T
A
C
C
G
T
A
C
G
C
G
C
G
C
G
A
T
T
A
T

21. TT
A
C
A
G
C
C
AA
G
DNA polymerase III
goes through the
nitrogen bases
connecting them.
T
A
T
A
G
TT
A
C
TT
T
T
A
C
C
G
T
A
C
G
C
G
C
G
C
G
A
T
T
A
T

22. T
A
C
A
C
C
T
A
G
C
C
A
C
G
C
C
G
C
T
A
The DNA strands
come together, then
you have 2 complete
DNA strands.
G
T
A
T
A
T
A
C
G
T
T
A
G
T
G
A
T
G
A

23. 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.

24. 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.