1. DNA Replication

2. Replication Facts DNA has to be copied before a cell divides
DNA is copied during mitosis and meiosis
New cells will need identical DNA strands

3. DNA Replication
Two strands of the DNA molecule open forming replication forks
New strands grow at the forks
Replication
Fork
Parental
DNA Molecule 3’ 5’

4. DNA Replication
As the 2 DNA strands open at the origin, replication bubbles form
Prokaryotes (bacteria) have a single bubble
Eukaryotic chromosomes have MANY bubbles
Bubbles

5. DNA Replication
Helicase “unzips” and separates the 2 DNA strands by breaking the weak hydrogen bonds
Binding proteins attach and keep the 2 DNA strands separated

6. DNA Replication
Before new DNA strands can form, there must be RNA primers present to start the addition of new nucleotides
DNA polymerase can then add the new nucleotides

8. Remember the Strands are AntiparallelO 1 2 3 4 5 P O 1 2 3 4 5 G C T A

9. Synthesis of the New DNA Strands
The leading strand is synthesized as a single strand from the point of origin toward the opening replication fork
RNA
Primer
DNA Polymerase
Nucleotides 3’ 5’

10. Proofreading New DNA
DNA polymerase initially makes about 1 in 10,000 errors
Other enzymes proofread and correct these mistakes
The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors

11. Semiconservative Model of Replication
The two strands of the parental molecule separate, and each acts as a template for a new strand
New DNA has 1 ORIGINAL and
1 NEW strand of DNA
DNA Template
New DNA
Parental DNA