1. 5’
3’
Adenine
Thymine
Cytosine
Guanine
Deoxyribo Sugar
Phosphate
3’
5’

2. DNA Helicase
DNA Helicase begins
to split the DNA.
Single strand proteins
come in to hold the
DNA stable
Single strand Protein

3. DNA Helicase continues to to
split the DNA as more Single
strand proteins come in.

4. DNA Helicase continues to to
split the DNA as more Single
strand proteins come in.

5. 5’
3’
DNA Polymerase III
starts putting new
nitrogen bases onto the
leading strand. It can
only synthesize from 3’
to 5’.
3’
5’

6. 5’
3’
3’
Polymerase III
continuously
synthesizes the
other half the the
leading strand.
5’

7. 5’
3’
3’
Polymerase III
continuously
synthesizes the
other half the the
leading strand.
5’

8. 5’
3’
3’
Polymerase III
continuously
synthesizes the
other half the the
leading strand.
5’

9. 5’
3’
3’
Now the leading strand
is done and it is time to
start the lagging strand.
5’

10. Because
Polymerase III
cannot
synthesize from
5’ to 3’, a RNA
primer is made
by Primase so
Polymerase III
can start on it.
3’
RNA Primer
Primase
5’

11. 3’
These fragments of
DNA are called
Okazaki fragments.
5’

12. 3’
Polymerase III starts
on the RNA primer
and sets the bases
towards the 5’.
5’

13. 3’
Polymerase III starts
on the RNA primer
and sets the bases
towards the 5’.
5’

14. 3’
Polymerase III starts
on the RNA primer
and sets the bases
towards the 5’.
5’

15. 3’
Polymerase I turns
the RNA primers into
phosphates.
Polymerase I
5’

16. Now there are two
new DNA helixes.