1. DNA Replication Biology 12

2. Two Jokes today….because I forgot last time!

3. What is DNA replication? Process by which DNA copies itself Before a cell starts mitosis, it replicates its DNA

4. Semi-Conservative Replication: Each strand acts as a template for a new double helix. Each new double-stranded molecule is composed of one parental strand and one new strand. Dds

5. Important: The two strands in DNA are anti-parallel One strand is in a 5' to a 3' while the other is in the opposite direction( 3' to 5' )

6. Short video clip (1 st time): http://www.youtube.com/watch?v=teV62zrm2P 0http://www.youtube.com/watch?v=teV62zrm2P 0

7. The Steps:

8. 1. Separation of Strands Weak hydrogen bonds that hold bases together are “unzipped” by an enzyme called DNA helicase

9. 2. Keeping the strand separated Single stranded binding proteins (SSBs) prevent the strands for sticking back together (reannealing)

10. Note: Replication proceeds only in the 5’ to 3’ direction (on the daughter strand)! This makes one side much simpler than the other.

11. 3. Building Complimentary Strands Primase creates a RNA primer which allows DNA polymerase to start attaching new nucleotides DNA polymerase continues until it reaches another RNA primer

12. 3. Building Complimentary Strands Leading strand Built continuously From parent 3’ end toward replication fork

13. 3. Building Complimentary Strands Lagging strand Built in short Okazaki fragments between RNA primers oDiscontinuous oFrom parent 3’ end oAway from replication fork

14. Another picture…. Okazaki fragments

15. 3. Building Complimentary Strands DNA ligase Joins Okazaki fragments together ▫Links all the new pieces of DNA together ▫Lagging strand only!

16. 4. Proofreading DNA polymerase checks for proper base pairing If mistake found: ▫Removes ▫Replace with proper nucleotide

17. Short video clip (2 nd time): http://www.youtube.com/watch?v=teV62zrm2P 0http://www.youtube.com/watch?v=teV62zrm2P 0

18. To do : Re-read page 217-222 Page 229: ▫Questions 1, 3-6, 9-15 Page 230 ▫Questions 3, 6, 10,13,14 Biology 12 is so much fun!