DNA STRUCTURE & REPLICATION

1. DNA STRUCTURE & REPLICATION

2. Chemical Inheritance

3. Protein or DNA? Protein Coat Viral Proteins Cells w/ viral DNA DNA Viruses cultured with radioactive sulfur source Protein Coat DNA Viral Proteins Cells w/ viral DNA Viruses cultured with radioactive phosphorous source

4. Structure - Base Pairing • A – T  2 H-bonds • G – C  3 H-bonds

5. Overall Structure

6. Replication is • Semiconservative

7. Origins of Replication • Humans can replicate 6 billion in few hours • Eukaryotes have multiple origins of replication

8. Replication Fork • Helicase • Breaks h-bonds between bases • Separates strands • Single-strand binding protein • Prevents reattachment • Primase • Adds RNA to template • Serves as attachment point for DNA polymerase

9. Adding Nucleotides • DNA Polymerase • Adds nucleotides to 3’ end of pre-existing strands

10. Adding Nucleotides

11. DNA Elongation • Leading strand • Replicated from a single primer • Lagging strand • Replicated in several segments due to unidirectional DNA polymerization • Ligase • Attaches Okazaki fragments

12. Replication Review Helicase and s-sbp’s open up original DNA Primase adds primers so DNA Polymerase can attach Okazaki fragments form as “bubble” elongates DNA polymerase replaces primers with DNA Ligase links together fragments 5’ 5’ 3’ Leading Strands 5’ 3’ 5’

13. Terminal Problems

14. 5’ 3’ 3’ 5’ Terminal Problems 3’ 5’ 5’ 3’ 5’ 3’ 5’ 3’ 3’ 5’ 5’ 3’

15. Telomeres • Non-coding segments on the ends of DNA • Not replicated due to inability of DNAP to attach to end. • Telomerase • Adds telomeres

16. Replication Review • What is the function of each of the enzymes involved in replication? • In what ways is the function of DNA polymerase limited? • Why do eukaryotic cells replicate DNA at an overall faster rate than prokaryotes? • Write an analogy for the relationship between helicase and ligase.