DNA replication is the process by which a cell makes an identical copy of its DNA before cell division. It occurs during the S phase of interphase and involves unwinding the DNA double helix, synthesizing new strands complementarily using existing strands as templates, and sealing the newly synthesized DNA. Key enzymes involved include DNA helicase, DNA polymerase, DNA primase, and DNA ligase. DNA polymerase adds nucleotides to the leading strand continuously but must add fragments called Okazaki fragments discontinuously to the lagging strand due to the anti-parallel nature of DNA replication.

1. By: Laken Poole

2. DNA Replication occurs before a cell
splits apart. The replication process
takes place during mitosis. To be more
specific, it takes place in a step of
mitosis called interphase. Interphase
has different steps also. DNA
replication takes place during the S
phase of interphase.

3. DNA replication is a process that is
very essential in every cell. If DNA
replication did not occur, cells
wouldn’t function properly. DNA
replication occurs so that when cells
divide, the new cells have the same
DNA as the cell they were made
from.

4. As you know, DNA is made up of two
strands. During DNA replication, an
enzyme called DNA helicase
“unzips” these two strands. These
two strands have different names,
which are the lagging and leading
strand.

5. The leading strand is synthesized
continuously in the 5 prime to 3
prime direction, while the lagging
strand is synthesized discontinuously
in the 5 prime to 3 prime direction.

6. DNA polymerase III adds nucleotides
to the end of a growing DNA strand.
DNA primase is an enzyme that
marks a starting point on the lagging
strand. DNA polymerase I removes
the starting point from the lagging
strand and replaces it with DNA.

7. DNA ligase joins Okazaki fragments,
which are short, newly synthesized
DNA fragments that are formed on
the lagging strand. DNA ligase also
seals repairs, and seals
recombination fragments. That is
how DNA replication occurs.

8. So you can get a better
understanding, the following slides
will demonstrate the entire DNA
replication process.

9. Helicase

10. 5’
A
T
T
Helicase
A
C
C
A
A
T
C
G
G
C
T
A
G
C
A
T
C
G
G
C
3’
G
T
3’
G
= Phosphate
= Sugar
= Adenine
= Thymine
= Cytosine
= Guanine
DNA replication begins when the
enzyme helicase unwinds and
breaks the bonds between the
nucleotides of the DNA molecule.
5’

11. A
5’
T
C
G
G
T
T
C
G
G
C
T
A
G
C
A
T
C
G
G
C
= Adenine
A
A
3’
= Phosphate
= Sugar
A
Helicase
C
3’
T
= Thymine
= Cytosine
= Guanine
5’

12. A
5’
T
= Phosphate
= Sugar
A
C
G
Helicase
C
G
= Adenine
A
T
A
G
G
C
T
A
G
C
A
T
C
G
G
C
= Thymine
T
C
3’
3’
T
= Cytosine
= Guanine
5’

13. A
5’
3’
T
T
C
G
C
G
T
Helicase
A
A
G
C
A
T
C
G
G
C
= Thymine
C
T
A
G
G
= Adenine
T
C
3’
= Phosphate
= Sugar
A
= Cytosine
= Guanine
5’

14. A
5’
3’
T
T
C
G
C
G
Helicase
T
= Adenine
A
= Thymine
T
A
C
G
G
C
T
A
G
C
A
T
C
3’
= Phosphate
= Sugar
A
G
G
C
= Cytosine
= Guanine
5’

15. A
5’
3’
T
T
C
G
C
G
T
A
A
Helicase
C
A
G
C
A
T
C
G
G
C
= Thymine
T
C
T
= Adenine
G
G
3’
= Phosphate
= Sugar
A
= Cytosine
= Guanine
5’

16. A
5’
3’
T
T
C
G
C
G
T
A
A
T
Helicase
= Adenine
= Thymine
G
C
G
A
G
C
A
T
C
G
G
C
= Cytosine
C
T
3’
= Phosphate
= Sugar
A
= Guanine
5’

17. A
5’
3’
T
T
C
G
C
G
T
A
A
T
C
G
Helicase
= Adenine
= Thymine
G
= Cytosine
C
T
C
A
T
C
G
G
C
= Guanine
A
G
3’
= Phosphate
= Sugar
A
5’

18. A
5’
3’
T
T
C
G
C
G
T
A
A
T
G
= Adenine
= Thymine
G
C
Helicase
T
= Cytosine
C
= Guanine
A
G
C
A
T
C
3’
= Phosphate
= Sugar
A
G
G
C
5’

19. A
5’
3’
T
T
C
G
C
G
T
A
A
T
= Adenine
= Thymine
G
C
G
= Cytosine
C
T
Helicase
G
A
= Guanine
A
C
T
C
3’
= Phosphate
= Sugar
A
G
G
C
5’

20. A
5’
3’
T
T
C
G
C
G
T
A
A
T
= Adenine
= Thymine
G
C
G
= Cytosine
C
Helicase
T
G
= Guanine
A
C
A
T
C
3’
= Phosphate
= Sugar
A
G
G
C
5’

21. 3’
A
T
T
5’
A
= Phosphate
= Sugar
G
C
C
G
T
A
A
= Adenine
= Thymine
T
= Cytosine
G
C
G
C
T
G
A
Helicase
C
T
C
3’
= Guanine
A
G
G
C
5’

22. 3’
A
T
T
5’
A
= Phosphate
= Sugar
G
C
C
G
T
A
A
= Adenine
= Thymine
T
= Cytosine
G
C
G
C
T
G
C
A
T
C
3’
= Guanine
A
G
Helicase
G
C
5’

23. T
T
G
C
G
T
A
A
T
C
G
G
T
= Phosphate
= Sugar
= Adenine
= Thymine
= Cytosine
C
= Guanine
A
G
C
A
T
C
3’
3’
A
C
5’
A
G
G
C
5’

24. T
T
G
C
G
T
A
A
T
C
G
G
T
= Phosphate
= Sugar
= Adenine
= Thymine
= Cytosine
C
= Guanine
A
G
T
C
G
G
C
Now there are two
complimentary strands of DNA.
C
A
3’
3’
A
C
5’
A
5’

25. DNAA
5’
T
Polymerase
III C
C
T
A
T
RNA Primer 3
A
G
DNA polymerase III is able to add
nucleotides continuously to the leading
strand of DNA. Meanwhile, the lagging
strand goes through many different
steps to add the nucleotides.
C
G
T
G
G
A
T
RNA
G
RNA Primer
Primase
C
Leading
Strand
Lagging
Strand
A
C
A
C
3’
T
G
G
C
5

26. T
T
5’
A
A
DNA
C
Polymerase
C
T
III
A
C
G
T
3’
T
RNA Primer 3
A
5’
G
As shown, RNA
primase adds an
RNA primer to the
lagging strand.
G
A
T
G
RNA Primer
RNA
C
A
Primase
G
A
T
C
3’
C
G
G
C
5

27. T
T
5’
A
3’
A
DNA
C
Polymerase
C
T
III
A
C
G
T
T
RNA Primer 3
A
G
5’
As shown, RNA
primase adds an
RNA primer to the
lagging strand.
G
A
T
G
C
RNA Primer
A
G
A
T
C
3’
C
G
G
C
RN
Prim
5

28. 3’
RNA Primer
T
T
T
A
A
C
5’
A
G
G
C
DNA
T
Polymerase
A
III
C
G
T
G
5’
A
T
Now, the RNA
primase is gone and
the next enzyme
takes over.
G
RNA Primer
C
A
G
C
A
T
C
3’
3
G
G
C
5

29. 3’
RNA Primer
T
T
T
A
A
C
5’
A
G
G
G
G
C
T
DNA
A
Polymerase
C
III
G
T
A
5’
Now, the RNA
primase is gone and
the next enzyme
takes over.
T
D
RNA Primer
C Polym
G
A
G
C
A
T
C
3’
3
G
G
C
5

30. 3’
RNA Primer
T
T
T
A
A
C
5’
A
G
G
G
G
A
A
C
T
A
DNA
Polymerase
C
G
III
T
T
5’
Now, the RNA
primase is gone and
the next enzyme
takes over.
DN
RNA Primer
C Polym
G
A
G
C
A
T
C
3’
3
G
G
C
5

31. T
T
RNA Primer
T
3’
A
C
5’
A
G
C
A
The next
enzyme is
DNA
polymerase I.
G
G
G
T
A
A
A
T
T
C
DNA
G
Polymerase
T
5’
G
DNA
RNA Primer
C
Polymerase
AI
G
C
A
T
C
3’
3
G
G
C
5

32. T
T
G
C
This enzyme
converts the
RNA into DNA
and
synthesizes
the lagging
strand in the
5’ to 3’
direction.
G
T
A
A
T
C
G
A
G
G
A
T
5’
C
A
T
C
3’
3
DNA G
RNA Primer
C
Polymerase
I A
G
T
DNA
G
Polymerase
RNA Primer
T
3’
A
C
5’
A
G
G
C
5

33. T
T
G
C
This enzyme
converts the
RNA into DNA
and
synthesizes
the lagging
strand in the
5’ to 3’
direction.
G
T
A
A
T
C
G
G
C
T
DNA
G
Polymerase
A
III
RNA Primer
T
3’
A
C
5’
A
A
G
G
A
DNA T
Polymerase
G
RNAI Primer
C
A
C
5’
T
C
3’
3
G
G
C
5

34. RNA Primer
T
3’
T
T
A
A
C
5’
A
G
G
C
G
T
A
T
C
C
T
A
DNA
G
Polymerase
A
III
C
3’
DNA G
A
Polymerase
I T
G
G
5’
A
G
C
3’
3
G
RNA Primer
C
A
5’
This enzyme
converts the RNA
into DNA and
synthesizes the
lagging strand in
the 5’ to 3’
direction.
C
T
G
C
5

35. T
T
RNA Primer
T
3’
A
C
5’
A
G
C
3
A
G
5’
DNA G
G
Polymerase
I A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
3’
C
A
DNA
C
Polymerase
G
3’
III
5’
RNA Primer
C
This enzyme
converts the RNA
into DNA and
synthesizes the
lagging strand in
the 5’ to 3’
direction.
A
C
T
G
C
5

36. T
T
3’
A
C
5’
A
G
C
5’
G
RNA Primer
T
3
DNA A
G
Polymerase
I G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
A
T
C
DNA
G
3’ Polymerase
3’
RNA Primer
C
A
This enzyme converts
the RNA into DNA and
synthesizes the
lagging strand in the
5’ to 3’ direction.
5’
C
T
G
C
5

37. T
T
A
C
5’
A
G
C
G
5’
3’
DNA
polymerase
I has
synthesized
as far as it
could. Now
it’s time for
the next
enzyme
RNA Primer
T
Polymerase 3
I A
C
G
C
G
T
A
A
T
C
G
T
A
T
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
G
DNA
3’
RNA Primer
C
A
5’
C
5

38. 5’
A
T
T
A
C
3’
G
C
5’
DNA
polymerase
I has
synthesized
as far as it
could. Now
it’s time for
the next
enzyme
Polymerase
RNA Primer
A
T
3
I A
T
G
C
G
T
A
A
T
C
G
C
G
T
A
T
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
G
DNA
C
3’
RNA Primer
C
A
5’
C
5

39. 5’
A
T
T
G
C
5’
DNA
polymerase
I has
synthesized
as far as it
could. Now
it’s time for
the next
enzyme
RNA I T
Primer
A
G
T
C
G
C
G
T
A
A
T
G
T
A
A
T
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
3
A
C
A
C
3’
G
G
G
DNA
C
3’
RNA Primer
C
A
5’
C
5

40. 5’
A
T
T
G
C
5’
DNA
polymerase
I has
synthesized
as far as it
could. Now
it’s time for
the next
enzyme
G
T
C
G
C
G
T
A
A
T
G
T
A
A
T
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
3
A
C
A
C
3’
RNA I T
Primer
A
G
G
G
DNA
C
3’
RNA Primer
C
A
5’
C
5

41. 5’
A
T
T
G
C
G
T
T
C
C
T
A
G
C
A
T
C
G
DNA
polymerase
I has
synthesized
as far as it
could. Now
it’s time for
the next
enzyme
G
G
3’
A
A
5’
G
DNA
C
3’
5’
* Note: The
short segment
of DNA that
was just
created is
called an
Okazaki
Fragment.
A
T
T
A
C
G
C
G
T
A
A
T
C
A
C
3’
G
3
RNA Primer
C
A
C
T
G
C
5

42. 5’
A
T
3’
5’
A
T
Which is…
T
A
T
A
C
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
G
G
G
C
C
3’
3
3’
RNA Primer
C
A
5’
C
5

43. 5’
A
T
3’
5’
A
T
Which is…
T
A
T
A
C
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
G
G
G
C
C
3’
3
3’
RNA Primer
C
A
5’
C
5

44. 5’
A
T
3’
5’
A
T
Which is…
T
A
T
A
C
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
G
G
G
C
C
3’
Ligas
5
3’
RNA Primer
C
A
5’
C
5

45. 5’
A
T
3’
5’
A
T
Which is…
T
A
T
A
C
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
G
G
G
C
C
3’
DNA
5
Ligase
3’
RNA Primer
C
A
5’
C
5

46. 5’
A
T
3’
5’
DNA
Ligase!!!!
A
T
T
DNA
A
Ligase
T
A
C
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
G
G
G
C
C
3’
3
3’
RNA Primer
C
A
5’
C
5

47. T
T
C
5’
A
C
3’
5’
A
T
A
T
DNA A
Ligase
G
C
G
C
G
T
A
A
T
C
G
G
Now, DNA ligase
forms a
phosphodiester
bond.
T
A
T
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
G
C
3
3’
RNA Primer
C
A
5’
C
5

48. 3’
5’
T
T
A
C
G
C
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
G
C
C
3’
Once it
does that,
it leaves.
3’
A
T
T
3
A
DNA
Ligase
G
RNA Primer
C
A
5’
C
5

49. A
T
T
A
C
3’
5’
T
T
A
G
C
G DNA
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
G
C
C
3’
Once it
does that,
it leaves.
3’
3
Ligase
RNA Primer
C
A
5’
C
5

50. A
T
T
A
C
3’
5’
T
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
G
C
C
3’
Once it
does that,
it leaves.
3’
3
DNA
Ligas
RNA Primer
C
A
5’
C
5

51. A
T
T
A
C
3’
5’
T
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
G
C
C
3’
Once it
does that,
it leaves.
3’
3
DNA
Ligas
RNA Primer
C
A
5’
C
5

52. A
T
T
A
C
3’
5’
T
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
G
C
C
3’
Once it
does that,
it leaves.
3’
3
D
Lig
RNA Primer
C
A
5’
C
5

53. A
T
T
A
C
3’
5’
T
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
G
C
C
3’
Once it
does that,
it leaves.
3’
3
RNA Primer
C
A
5’
C
5

54. T
T
3’ Now, the 5’
next
A
C
5’
A
G
C
G
T
T
A
C
G
C
enzyme,
which we
had
already
seen
before…
A
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
G
C
3
3’
RNA Primer
C
A
5’
C
3

55. T
T
C
5’
A
C
5’
3’
A
T
A
T
A
G
C
G
C
G
Is????
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
G
C
3
3’
RNA Primer
C
A
5’
C
R
3

56. T
T
C
5’
A
C
5’
3’
A
T
A
T
A
G
C
G
C
G
Is????
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
G
C
3
3’
RNA Primer
C
A
5’
C
RNA
3

57. T
T
C
5’
A
C
5’
3’
A
T
A
T
A
G
C
G
C
G
Is????
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
C
3
3’
RNA Primer
C
A
RNA
3
Primase
C
G
5’

58. T
T
G
3’
5’
A
C
5’
A
C
G
T
T
Yep… RNA
primase. The
cycle that had
just
happened,
begins again!
A
A
C
G
C
G
T
A
T
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
C
3
3’
RNA Primer
C
A
5’
RNA
G
Primase 3
C

59. T
T
C
5’
A
C
3’
5’
A
T
A
T
A
G
C
G
C
G
T
A
A
T
C
G
G
Remember,
RNA primase
adds an RNA
primer to the
lagging strand.
T
A
T
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
C
3
3’
RNA Primer
C
A
5’
RNA
G
Primase
C
5

60. T
T
C
5’
A
C
3’
5’
A
T
A
T
A
G
C
G
C
G
T
A
A
T
C
G
G
Remember,
RNA primase
adds an RNA
primer to the
lagging strand.
T
A
T
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
C
3
3’
RNA Primer
C
A
5’
RNA
G
RNA Primer 5
Primase
C

61. T
T
5’
A
3’
5’
A
C
C
G
G
T
T
The RNA
primase
leaves,
once again.
A
A
C
G
C
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
C
3
3’
RNA Primer
C
A
5’
RNA
G
RNA Primase 3
Primer
C

62. T
T
5’
A
3’
5’
A
C
C
G
G
T
T
The RNA
primase
leaves,
once again.
A
A
C
G
C
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
G
C
3
3’
RNA Primer
C
A
5’
RNA
RNA Primer 3
C

63. T
T
5’
A
3’
5’
A
C
C
G
G
T
T
The RNA
primase
leaves,
once again.
A
A
C
G
C
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
3’
A
G
G
G
C
3
3’
RNA Primer
C
A
5’
RNA Primer R
3
C

64. A
T
T
5’
3’
A
T
T
A
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
G
C
C
C
3’
G
Leaving us to
the next
enzyme.
3’
3
RNA Primer
C
A
5’
RNA Primer 3
C

65. A
T
T
A
C
3’
G
5’
T
T
A
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
G
C
C
3’
Do you
remember
what that
is?
3’
3
RNA Primer
C
A
5’
RNA Primer 3
C

66. A
T
T
A
C
3’
G
5’
T
T
A
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
G
C
C
3’
Do you
remember
what that
is?
3’
3
RNA Primer
C
A
5’
RNA Primer 3
C
Po

67. A
T
T
A
C
3’
5’
T
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
C
D
RNA Primer 3
C
Poly
C
3’
Did you
guess yet?
3’
3
RNA Primer
C
A
G
5’

68. A
T
T
A
C
G
5’
3’
T
T
A
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
C
A
T
T
C
5’
A
G
G
C
C
3’
Do you
remember?
3’
3
RNA Primer
C
A
5’
DNA
G
Polymer
RNA Primer 3
C

69. A
T
T
C
3’
5’
T
A
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
A
T
C
5’
A
G
G
C
C
3’
3’
Did you get it right?
DNA polymerase I is
back again to
synthesize this part of
the DNA strand.
5’
3
RNA Primer
C
A
C
T
DNA
G
Polymerase
RNA Primer 3
I C

70. T
T
5’
A
A
C
C
G
G
Adding
corresponding
nucleotides to
the strand.
A
C
G
C
5’
T
T
3’
A
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
A
T
C
3’
A
G
G
C
3
RNA Primer
C
A
C
5’
DNA T
Polymerase
G
RNA Primer 5
I C
3’

71. T
T
5’
A
A
C
C
G
G
Adding
corresponding
nucleotides to
the strand.
A
C
G
C
5’
T
T
3’
A
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
A
T
C
3’
A
G
G
C
3
RNA Primer
C
A
5’
DNA
C
Polymerase
T
I
G
RNA Primer 5
3’
C

72. T
T
5’
A
A
C
C
G
G
G
C
Adding
corresponding
nucleotides to
the strand.
A
C
5’
T
T
3’
A
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
A
T
C
3’
A
G
G
C
3
RNA Primer
C
DNA A
Polymerase
C
I T
C
5’
3’
G
G
RNA Primer 5
C

73. T
T
5’
A
A
C
C
G
G
G
C
Adding
corresponding
nucleotides to
the strand.
A
C
5’
T
T
3’
A
G
T
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
3
DNA C
RNA Primer
G
Polymerase
A
G I
C
5’
3’
RNA Primer 5
C
G

74. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
G
C
G
T
A
A
T
5’
3’
And
replacing
the RNA
with DNA.
T
A
T
C
G
G
C
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
3
DNA G
RNA Primer
G
C
Polymerase
T I
A
C
5’
3’
RNA Primer 5
C
G

75. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
C
G
T
A
T
A
G
5’
3’
And
replacing
the RNA
with DNA.
T
A
T
C
G
G
C
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
3
5’
DNA T
A
Polymerase
G
C
RNA Primer
G I
C
3’
RNA Primer 5
C
G

76. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
G
C
G
T
A
T
A
A
T
C
G
G
And then it’s
leaves again
after
finishing its
job..
A
G
5’
C
T
3’
T
T
A
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
3
5’
3’
DNA
G
C
Polymerase
G
C
I
RNA Primer 5
C
G

77. T
T
A
C
5’
A
G
C
G
5’
And then it’s
leaves again
after
finishing its
job..
T
T
3’
A
A
C
G
C
G
T
A
T
T
A
T
A
C
G
C
G
C
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
3
Meanwhile…
G
T
5’
3’
DNA
Polymer
C
A
I
G
RNA Primer 5
C
G

78. T
T
C
5’
A
C
T
A
T
A
T
A
G
C
G
G
C
G
A
T
A
A
T
3’
5’
DNA ligase
returns yet again
to form another
phosphodiester
bond.
A
C
G
G
C
T
A
G
C
G
T
A
T
C
G
C
G
G
C
DN
Liga
C
A
3’
T
3
C
G
T
5’
3’
DNA
Polymer
C
A
I
G
RNA Primer 5
C
G

79. A
T
T
C
T
A
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
DNA
D
Ligas
G
C
G
C
Polym
T
A
T
A
G
C
G
C
A
T
A
T
C
5’
A
G
C
G
G
C
C
3’
3’
5’
DNA ligase
returns yet again
to form another
phosphodiester
bond.
5’
3’
3
RNA Primer 5
C
G

80. A
T
T
C
T
A
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
T
A
G
5’
A
C
3’
5’
DNA ligase
returns yet again
to form another
phosphodiester
bond.
G
D
Polym
DNA
C
Ligase
T
A
C
G
C
A
T
A
T
C
3’
3
G
C
G
G
C
5’
3’
RNA Primer 5
C
G

81. A
T
T
C
T
A
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
G
C
T
A
G
C
G
A
T
A
T
C
5’
A
G
C
G
G
C
C
3’
3’
5’
DNA ligase
returns yet again
to form another
phosphodiester
bond.
5’
3’
3
DNA G
G Ligase C
C
T
DN
A
Polym
C
I
RNA Primer 5
C
G

82. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
G
C
G
T
A
A
T
3’
5’
Remember,
DNA
polymerase
I has the job
of replacing
RNA with
DNA.
T
A
T
C
G
G
C
T
A
G
C
G
A
T
A
C
3’
A
G
C
G
C
DNA G
G LigaseC
C
T
5’
3’
3
DNA
C
Polyme
T
I
A
G
RNA Primer 5
C
G

83. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
C
G
T
A
T
5’
3’
While the
DNA ligase
leaves.
G
T
A
T
A
C
G
C
G
C
G
T
A
G
C
A
T
C
3’
A
G
G
C
T
3’
G
DNA
Ligase
C
A
DNA
Polymeras
T
A
C
G I
RNA Primer 5
C
G
G
5’
3
C

84. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
C
G
T
A
A
T
G
3’
5’
The DNA
polymerase
I is replacing
the RNA
with DNA.
T
A
T
C
G
C
G
G
C
G
C
DNA
T
A
T
Ligase
A
G
C
G
C
A
T
C
3’
A
G
G
C
3
T
DNA
C
G
Polymerase
RNA Primer 5
G
IC
A
5’
3’

85. A
T
T
C
T
A
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
5’
A
G
C
G
C
C
3’
3’
5’
5’
3’
3
DNA
Ligas
DNA
G
Polymerase
5
C
G

86. A
T
T
C
T
A
T
A
G
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
5’
A
G
C
G
C
C
3’
3’
5’
5’
3’
3
L
DNA
G
Polymerase
5
C
G

87. T
T
C
5’
A
C
T
A
T
A
T
A
G
C
G
G
C
G
A
T
A
A
T
3’
5’
Then it leaves
after the job
is done.
A
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
3’
T
G
C
G
C
3
5’
3’
G
DNA
5
C
Polyme
G

88. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
G
C
G
T
A
A
T
3’
5’
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
G
C
3
Then it leaves
after the job
is done.
5’
3’
5D

89. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
G
C
G
T
A
A
T
C
G
G
C
T
A
3’
5’
T
A
T
C
G
G
C
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
G
C
3
The DNA
ligase has yet
one last bond
to form!
5’
3’
D
Lig
5

90. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
G
C
G
T
A
A
T
3’
5’
The DNA
ligase has yet
one last bond
to form!
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
G
C
3
5’
3’
DN
Liga
5

91. A
T
T
C
T
A
T
A
G
C
G
G
C
G
T
A
T
A
A
5’
A
T
A
T
C
G
G
C
T
A
C
3’
5’
The DNA
ligase has yet
one last bond
to form!
C
G
C
T
A
G
C
G
C
A
T
A
T
C
3’
G
G
C
G
G
C
G
C
3
5’
3’
DNA
Ligase
5

92. A
T
T
C
T
A
T
A
G
C
G
G
C
G
T
A
T
A
A
5’
A
T
A
T
C
G
G
C
T
A
C
3’
5’
The DNA
ligase has yet
one last bond
to form!
C
G
C
T
A
G
C
G
C
A
T
A
T
C
3’
G
G
C
G
C
3
5’
3’
G
G
DNA
Ligase
C
5

93. A
T
T
A
C
G
3’ The DNA 5’
T
ligase has yet
one last bond
to form!
T
A
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
5’
A
G
C
G
C
C
3’
5’
3’
G
G
DNA
Ligase
C
3
5

94. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
C
G
T
A
5’
3’
As it
finishes
it’s last
job…
G
T
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
C
3
5’
3’
DNA G
GLigase C
5

95. A
T
T
A
C
G
T
T
A
C
G
G
C
G
T
A
T
A
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
5’
A
G
C
G
C
C
3’
5’
3’
As it
finishes
it’s last
job…
5’
3’
DNA G
GLigase C
3
5

96. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
C
G
5’
3’
Then it
leaves
again.
G
T
T
A
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
3
G
G
C
5’
3’
G
DNA
C
5

97. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
C
G
5’
3’
Then it
leaves
again.
G
T
T
A
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
G
C
3
5’
3’
DNA
5

98. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
C
G
5’
3’
Then it
leaves
again.
G
T
T
A
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
G
C
3
5’
3’
5

99. T
T
C
5’
A
C
A
T
A
T
A
G
C
G
C
G
5’
3’
Then it
leaves
again.
G
T
T
A
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
G
C
3
5’
3’
5

100. T
T
A
C
5’
A
G
C
G
3’
5’
Now we are
left with two
identical
strands of DNA.
A
T
T
A
C
G
C
G
T
T
A
A
T
A
T
C
G
C
G
G
C
G
C
T
A
T
A
G
C
G
C
A
T
A
T
C
3’
A
G
C
G
G
C
G
C
3
5’
3’
5

101. Keep in mind that the
DNA molecules are in a
twisted shape.

102. Like this…

103. So really
we are
left with
this.

104. What would
happen if a mistake
were made during
the replication
process???

105. Sometimes, during DNA replication,
nucleotide bases are incorrectly paired.

106. Naturally, during DNA replication, the
mistakes are fixed.

107. Sometimes, however, the mistakes
cannot be fixed and they become
mutations.

108. They become permanent mutations
after the next cell division. This is
because once these mistakes have
been established, the cell no longer
recognizes them as errors.

109. Special Vocabulary:
• Telomeres- Telomeres are structures found at the end
of chromosomes.
• Okazaki fragments- Okazaki fragments are short,
newly formed DNA segments.
• DNA ligase- DNA ligase forms a phosphodiester bond,
joining the Okazaki fragments into a
continuous strand of DNA.

110. Special Vocabulary:
• Telomerase- Telomerase is an enzyme that is
especially found in cancer cells. This
enzyme adds nucleotides to telomeres.
• Cancer- Cancer is a disorder when some of the body’s
cells lose the ability to control growth.
• Transplanted cells- Transplanted cells are injected
into your body to replace
damaged or diseased cells.

111. Special Vocabulary:
• Cloning- Cloning is making genetically identical cells
that were produced from a single cell.
• Aging- Aging is the process of growing older.

112. THAT’S THE END OF
THE DNA
REPLICATION
PROCESS

113. Thanks for
watching!!! 