1. DNA Replication

2. Watson and Crick noticed the huge benefit of double strands Each strand can serve as a template for making for making the other

3. DNA Replication Prior to mitosis and meiosis DNA must be copied Like cells, all DNA comes from previously existing DNA

4. Semiconservative Model Each strand serves as a template for the creation of a new strand of DNA 2 DNA molecules are created, each containing 1 strand of the original DNA

5. Semiconservative Replication

6. The Beginning Topoisomerase unwinds the helix Helicase separates the strands Single stranded binding proteins (SSBs) keep the strands separated

7. Topoisomerase, Helicase and Single-Strand Binding Protein

8. Priming DNA A short RNA primer is added first by primase DNA can only be added to an existing primer

9. DNA Polymerases Each nucleotide is added one by one by DNA polymerases A added to T G added to C etc.

10. Antiparallel DNA Strands The two strands are arranged in opposite directions Each strand has an “end”

11. The Leading Strand Built continuously as the replication fork opens in front of it

12. The Lagging Strand Built in pieces the opposite direction of replication Built in fragments, called Okazaki fragments

14. Review Helicase separates strands, SSBs help keep strands apart DNA polymerase adds nucleotides DNA ligase fuses Okazaki fragments of lagging strands together

16. Topoisomerase Helicase Single Stranded Binding Proteins

17. Primase 3’ 5’ DNA Polymerase Leading Strand Lagging Strand Okazaki Fragments DNA Ligase