DNA replication is the process by which DNA copies itself during cell division. It occurs in three main stages: first, DNA helicase unwinds the double helix at the origin of replication; then, RNA primase constructs an RNA primer to mark the starting point for DNA polymerase to synthesize new strands of DNA by adding nucleotides; and finally, DNA ligase seals the DNA strands by forming phosphodiester bonds between nucleotides. DNA replication ensures each new cell formed during cell division contains an identical copy of the DNA code.

1. DNA Replication
By: Alli Ishman

2. 3’
5’
DNA Replication is the duplication
of DNA during cell division.
Replication takes place in the
nucleus and starts at the origin of
replication.
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
5’
3’
Cytosine

3. DNA Helicase unwinds doublestranded DNA at the origin of
replication by breaking
hydrogen bonds between
complementary strands. In
more simple terms, it is kind of
like a zipper unzipping.
DNA Helicase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

4. DNA Helicase unwinds doublestranded DNA at the origin of
replication by breaking
hydrogen bonds between
complementary strands. In
more simple terms, it is kind of
like a zipper unzipping.
DNA Helicase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

5. DNA Helicase unwinds doublestranded DNA at the origin of
replication by breaking
hydrogen bonds between
complementary strands. In
more simple terms, it is kind of
like a zipper unzipping.
DNA Helicase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

6. DNA Helicase unwinds doublestranded DNA at the origin of
replication by breaking
hydrogen bonds between
complementary strands. In
more simple terms, it is kind of
like a zipper unzipping.
DNA Helicase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

7. DNA Helicase unwinds doublestranded DNA at the origin of
replication by breaking
hydrogen bonds between
complementary strands. In
more simple terms, it is kind of
like a zipper unzipping.
DNA Helicase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

8. DNA Helicase unwinds doublestranded DNA at the origin of
replication by breaking
hydrogen bonds between
complementary strands. In
more simple terms, it is kind of
like a zipper unzipping.
DNA Helicase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

9. DNA Helicase unwinds doublestranded DNA at the origin of
replication by breaking
hydrogen bonds between
complementary strands. In
more simple terms, it is kind of
like a zipper unzipping.
DNA Helicase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

10. DNA Helicase unwinds doublestranded DNA at the origin of
replication by breaking
hydrogen bonds between
complementary strands. In
more simple terms, it is kind of
like a zipper unzipping.
DNA Helicase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

11. DNA Helicase unwinds doublestranded DNA at the origin of
replication by breaking
hydrogen bonds between
complementary strands. In
more simple terms, it is kind of
like a zipper unzipping.
DNA Helicase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

12. 5’
3’
Single-strand binding
proteins react with the
single-stranded regions of
the DNA and stabilize it.
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine
Single-strand binding
protein
3’
5’

13. An RNA primase constructs an
RNA primer to mark a starting
point.
RNA Primase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

14. DNA Polymerase III can then add
deoxyribonucleotides to synthsize
the new complementary strand of
DNA. The leading strand adds
nucleotides going down in the
animation shown, and the lagging
strand adds nucleotides going up in a
discontinues fashion.
RNA Primer
DNA Polymerase III
RNA Primase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

15. DNA Polymerase III can then add
deoxyribonucleotides to synthsize
the new complementary strand of
DNA. The leading strand adds
nucleotides going down in the
animation shown, and the lagging
strand adds nucleotides going up in a
discontinues fashion.
RNA Primer
DNA Polymerase III
RNA Primase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

16. DNA Polymerase III can then add
deoxyribonucleotides to synthsize
the new complementary strand of
DNA. The leading strand adds
nucleotides going down in the
animation shown, and the lagging
strand adds nucleotides going up in a
discontinues fashion.
RNA Primer
DNA Polymerase III
RNA Primase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

17. DNA Polymerase III can then add
deoxyribonucleotides to synthsize
the new complementary strand of
DNA. The leading strand adds
nucleotides going down in the
animation shown, and the lagging
strand adds nucleotides going up in a
discontinues fashion.
RNA Primer
DNA Polymerase III
RNA Primase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

18. When the DNA polymerase
III reaches the RNA primer
on the lagging strand it is
replaced by DNA polymerase
I.
RNA Primer
DNA Polymerase III
RNA Primase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

19. DNA polymerase I removes the
RNA and replaces it with DNA.
DNA Polymerase I
RNA Primer
DNA Polymerase III
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

20. DNA ligase then attaches and
forms phosphodiester bonds.
This is just a bond between the
phosphate of one nucleotide to
the sugar of another
nucleotide.
DNA Polymerase I
RNA Primer
DNA Polymerase III
DNA ligase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

21. DNA ligase then attaches and
forms phosphodiester bonds.
This is just a bond between the
phosphate of one nucleotide to
the sugar of another
nucleotide.
DNA Polymerase I
RNA Primer
DNA Polymerase III
DNA ligase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

22. DNA Polymerase I
RNA Primer
DNA Polymerase III
DNA ligase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

23. DNA Polymerase I
RNA Primer
DNA Polymerase III
DNA ligase
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

24. The DNA is further unwound, new
primers are made, and DNA
polymerase III begins synthesizing
other okazaki fragments. Okazaki
fragments are just short
fragments of DNA made on the
lagging strand during replication.
RNA Primer
DNA Polymerase III
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

25. The DNA is further unwound, new
primers are made, and DNA
polymerase III begins synthesizing
other okazaki fragments. Okazaki
fragments are just short
fragments of DNA made on the
lagging strand during replication.
RNA Primer
DNA Polymerase III
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

26. The DNA is further unwound, new
primers are made, and DNA
polymerase III begins synthesizing
other okazaki fragments. Okazaki
fragments are just short
fragments of DNA made on the
lagging strand during replication.
RNA Primer
DNA Polymerase III
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

27. Again, once DNA
polymerase III reaches the
RNA primer it is replaced
by DNA polymerase I.
RNA Primer
DNA Polymerase III
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

28. DNA polymerase I removes
the RNA primer.
DNA Polymerase I
RNA Primer
DNA Polymerase III
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

29. DNA ligase then attaches and forms
phosphodiester bonds. This is just a
bond between the phosphate of
one nucleotide to the sugar of
another nucleotide.
DNA ligase
DNA Polymerase I
RNA Primer
DNA Polymerase III
Phosphate
Sugar (Deoxyribose)
Adenine
Guanine
Cytosine

30. DNA ligase then attaches and forms
phosphodiester bonds. This is just a
bond between the phosphate of
one nucleotide to the sugar of
another nucleotide.
DNA ligase
DNA Polymerase I
RNA Primer
DNA Polymerase III
Sugar (Deoxyribose)
Phosphate
Adenine
Thymine
Guanine
Cytosine

31. DNA ligase then attaches and forms
phosphodiester bonds. This is just a
bond between the phosphate of
one nucleotide to the sugar of
another nucleotide.
DNA ligase
DNA Polymerase I
RNA Primer
DNA Polymerase III
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

32. DNA ligase
RNA Primer
DNA Polymerase III
Phosphate
Sugar (Deoxyribose)
Adenine
Thymine
Guanine
Cytosine

33. 5’
3’
3’
5’

34. What happens in DNA Replication?
First DNA helicase unwinds the double helix
shape of DNA. Then an RNA Primase constructs
an RNA primer to mark a starting point. DNA
polymerase III then adds nucleotides to make
the new strand of DNA. When DNA polymerase
III reaches the RNA primer, DNA polymerase I
comes in and removes the primer and finally
DNA ligase then attaches and forms
phosphodiester bonds. DNA replication occurs
during S phase in the nucleus.

35. In my own words
• Telomeres- keep ends of various chromosomes in the cell
from accidentally becoming attached to each other
• Okazaki Fragments- a section of the synthesized DNA on
the lagging strand
• DNA Ligase- stick the okazaki fragments together like glue
• Telomerase- an enzyme that adds telomere repeat
sequence
• Cancer- tissue that is able to grow in large amounts quickly
• Transplanted Cells- cells that have been taken, added to
and then given back
• Cloning- taking a piece of something and making another
copy
• Aging- the steady shrinking of cells in the body

36. Why does DNA replicate?
If DNA did not replicate then there would be no
DNA to pass on to the next generation, no way
to provide the cell with the information
necessary for processes, and no way to maintain
the cell’s living.

37. Mistakes (Mutations)
• DNA mutations happen when there are changes
in the nucleotide sequence that makes up the
strand of DNA. This can be cause by random
mistakes in DNA replication or even an
environmental influence like UV rays or
chemicals. Changing even just one nitrogen base
in a sequence can change the amino acid that is
expressed by the DNA codon which can lead to a
completely different protein being expressed.
These mutations range from being non-harmful
all the way up to causing death.

38. Works Cited
• http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/si
tes/dl/free/0072437316/120076/micro04.swf::DNA
Replication Fork
• http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/si
tes/dl/free/0072437316/120076/bio23.swf::How
Nucleotides are Added in DNA Replication
• “DNA Helix.” Photograph. “Nucleobases and
Their Production during the Photolysis of
Astrophysically-relevant Ices.” The Astrophysics
& Astrochemistry Lab. NASA Ames Research
Center, 2013. Web. 7 February 2014.