1. DNA Replication

2. Replication Occurs during cell division Must be accurate

3. Semiconservative Replication Each strand serves as a template for new strand Each new molecule has one parent strand and one new strand

4. Replication Process Replication begins when proteins bind to replication origin –Specific genomic sequence DNA Helicase unwinds double helix Strands kept apart by single stranded binding proteins Replication goes in both directions from origin

7. Details DNA is always synthesized 5’ to 3’ –Nucleotides added to 3’ end by DNA polymerase III Primase makes RNA primer allowing DNA polymerase to start elongation –Polymerase III can’t start a new strand itself

9. Synthesis Because DNA is made 5’ to 3’, only one strand is synthesized continuously –Leading strand Other strand is built discontinuously –Lagging strand –Built in small fragments called Okazaki fragments

11. Finishing Touches DNA polymerase I removes RNA primers –Replaces them with nucleotides DNA ligase joins Okazaki fragments

13. Repair Polymerase I and polymerase III act as quality control –Proofread sequence against template These enzymes can act as exonucleases –Backtrack and remove incorrect nucleotide, replacing it with correct one