1. DNA Replication
“A Play”

2. The Cast Replication Bubbles Replication Forks Helicase Primase
RNA Primer
DNA Polymerase
Leading Strand
Lagging Strand
Okazaki Fragments
DNA Ligase
Telomeres

3. Replication Bubble
DNA is unwound at certain sites called replication origins
The unwinding forms a replication bubble where replication will take place by using the exposed DNA strands as templates
Replication Bubbles form at many sites along the DNA molecule in order to make replication as fast a possible!

4. Replication Forks
Replication Bubbles have two replication forks
The Replication Fork is where the new strands of DNA will develop

5. Helicase An enzyme that unwinds and separates the DNA
Works just ahead of the replication fork to keep replication moving quickly along the entire DNA molecule

6. Primase
An enzyme that joins an RNA primer to the template DNA strand to start replication

7. RNA Primer
DNA cannot start a new DNA strand using the template strand of DNA unless it has something to attach to.
RNA primer is a made up of a few nucleotides that are complementary to the DNA template and can serve as a starting point for replication
Remember RNA has Uracil instead of Thymine…so A would bond with U

8. DNA Polymerase An enzyme with many functions
1. Adds new nucleotides to 3’ end of elongating strand
2. Dismantles RNA primer
3. Proofreads base pairing

9. Leading Strand DNA can only be synthesized in a 5’ to 3’ direction
Since the template strands run antiparallel this means that only one strand can be replicated continuously as the replication fork is separating
This strand is called the leading strand

10. Lagging Strand
Because DNA is replicated in only the 5’ to 3’ one strand must be replicated discontinuously
This is known as the lagging strand
This is done by building Okazaki fragments and then joining them together

11. Okazaki Fragments
Short Fragments of DNA that make up the lagging strand because it is replicated discontinously
Each Okazaki Fragment requires its own RNA primer
The Okazaki Fragments must be joined together for replication of the lagging strand to be complete

12. DNA Ligase
The enzyme that joins DNA fragments (mainly Okazaki Fragments) together

13. The Action

14. One Final Step
After ligase joins the gaps between Okazaki fragments and the gaps where replication bubbles meet one more thing must happen
DNA polymerase proofreads the new DNA strand to make sure that complementary base pairing is correct
DNA polymerase cuts out any incorrect base pairing on the new strand and replaces it with the proper base

15. Wait! There’s a little problem!
The RNA primer at the 5’ end of the daughter strand must be removed
Once this is done there is nothing for any new DNA nucleotides to attach to to fill in the gap.
This means the new DNA strand is slightly shorter (about 100 base pairs)

17. So, what does that mean?
The loss of genetic material could be disastrous and even result in cell death
Luckily there are special regions at the end of DNA that helps this problem

18. Telomeres
Telomeres are stretches of repetitive nucleotides that act as a buffer zone
Telomeres do not direct cell development
The erosion of telomeres helps protect against the loss of other genetic material
The complete erosion of telomeres can cause the loss of important genetic material or cell death
Telomeres can be extended using the enzyme telomerase