1. Sugar Phosphate Backbone
A C G T G C T G G A T T C C G A
Twisted
Double
Helix
T G C A C G A C C T A A G G C T
In this slide you can see the DNA Double Helix molecule. It is composed of a
Sugar Phosphate Backbone and several nitrogen bases called nucleotides.
= Adenine = Guanine
= Thymine = Cytosine

2. A Leading Strand
C
G
T
G C T G G A T T C C G A
Helicase
C G A C C T A A G G C T
A
C
G
T
Lagging Strand
In this slide you see that the enzyme Helicase comes in and starts to
unravel the Double Helix into the “Leading Strand” and the “Lagging
Strand.”

3. A
C
G
T
G
C
T G G A T T C C G A
Single
Stranded
Binding
Proteins
A C C T A A G G C T
G
C
A
C
G
T
In this slide you can see that as the Helicase unzips the DNA strand
Single Stranded Binding Proteins come in and hold the strands apart.

4. A
C
G
T
G
C T
G
G A T T C C G A
RNA Polymerase
T A A G G C T
C
C
A
G
C
A
C
G
T
In this slide you can see that an RNA Polymerase called a primase comes in and
constructs an RNA Primer, which is a sequence of nucleotides.

5. A DNA Polymerase III
C
G
T
G
C T
G
T G A T T C C G A
G C
RNA Primer
T A A G G C T
C
C
A
G
C
A
C
G
T
Then DNA Polymerase III comes in and starts to add Deoxyribonucleotides to start the
new complimentary strand of DNA.

6. A
C G
T G
C T
G
G A
T T
G T C C G A
C
A C G
A
A G G C
T
T A
C
C
G A
C
A
C
G
T
In this slide you can see how the DNA Polymerase III starts to add the
Deoxyribonucleotides.

7. A
C G
T G
C T
G
G A
T T
G T C C G A
C
A C G
A
A G G C
G
C T A
A T
C
C
G A
C
A
C
G RNA Polymerase
T
RNA Primer
Since DNA Polymerase III can only add nucleotides from the 3’ to the
5’ end, an RNA Primase must continuously add RNA primers (a.k.a.
Okazaki Fragment) to keep the DNA Polymerase going.

8. A
C G
T G
C T
G
G A
T T
G T C C G A
C
A C G
A
A G G C
G
C T A
A T
C
C
G A
C
A
C
G
T
The RNA Polymerase adds another RNA Primer to the “Lagging Strand”
so DNA Polymerase III can add the remaining nucleotides.

9. A
C G
T G
C T
G
G A
T T
G T C C G A
C
A C G
A
G
T
C
G
A G G C
G
C T A
A T
C
C
G A
C
A
C DNA Ligase
G
T

10. A
C G
T G
C T
G
G A
T T
G T C C G A
C
A C G
A
G
T
C
G
A G G C
G
C T A
A T
C
C
G A
C
A
C
G DNA Ligase
T
At this point in replication, DNA Polymerase I or “DNA Ligase” must fill in the
remaining nucleotide to finish the sequence.

11. A
C G
T G
C T
G
G A
T T
G T C C G A
C
A C G
New nucleotide A
G
T
C
G
T G G C
G A
C T A
A T
C
C
G A
C
A
C
G
T
This is the end of DNA Replication, the process repeats several times to
complete the cycle.