1. DNA Deoxyribo Nucleic Acid

2. DNA or Proteins? Scientists debated which was the genetic material A couple of experiments showed that altering DNA changed an organisms make up

3. Experimental Evidence Avery-MacLeod- McCarty experiment showed that DNA could transform bacteria Hershey-Chase experiments showed that viruses insert DNA into hosts, not proteins

4. Avery-MacLeod-McCarty

5. Hershey-Chase

6. DNA is Made of Nucleotides Nitrogenous Base (determines whether nucleotide is A, T, G or C) Deoxyribose sugar Phosphate group

7. Solving the Structure of DNA Solved by relatively unknown biologists James Watson and Francis Crick (and Rosalind Franklin) They published their theory in a one-page paper

9. The Ribose-Phosphate Backbone Ribose sugar of one nucleotide connects to the phosphate group of the next Bonds are called phosphodiester bonds

11. The Two Types of Bases Purines 2 ringed nitrogenous base Adenine and guanine Pyrimidines 1 ringed nitrogenous base thYmine and cYtosine

12. Base Pairing 2 hydrogen bonds form between adenine and thymine 3 hydrogen bonds form between cytosine and guanine Notice a purine always bonds with a pyrimidine

13. The Double Helix Discovered by Watson and Crick The two strands are held together by hydrogen bonding between base pairs

14. Chromosomes A single molecule of DNA Eukaryotes usually have many linear chromosomes Prokaryotes usually have one circular chromosome Prokaryotes also have plasmids

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

16. 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

17. Semiconservative Replication

18. DNA Replication is Remarkably Fast and Accurate! Humans have 46 chromosomes, and thus 46 DNA molecules About 6 billion base pairs DNA replication takes just a few hours, even in humans Only 1 error per 1 billion nucleotides

19. The Basics of DNA Replication Requires more than a dozen enzymes and proteins Appears to operate pretty similarly in prokaryotes and eukaryotes (except DNA is in one circular molecule in prokaryotes)

20. Origins of Replication Replication begins in hundreds to thousands of sites at once in eukaryotes Replication occurs in both directions

22. The Beginning Topoisomerase unwinds the helix Helicase separates the strands Single stranded binding proteins (SSBs) keep the strands separated This forms a replication fork

23. Topoisomerase, Helicase and Single-Strand Binding Protein

24. DNA Polymerases Each nucleotide is added one by one by DNA polymerases Nucleoside Triphosphates are added Nucleoside loses 2 phosphate groups, providing energy to synthesize new strand

25. Antiparallel DNA Strands The two strands are arranged in opposite directions 3' end contains hydroxyl group 5' end contains phosphate group Nucleotides are ONLY added to the 3' end of a strand

26. The Leading Strand Synthesis always occurs in the 5' to 3' direction (the 5' end of the new strand is synthesized first) (attaches to the 3’ end of the template) One strand can grow continuously as the fork opens in front of it

27. The Lagging Strand Built discontinuously in the opposite direction of replication Built in fragments, called Okazaki fragments DNA ligase connects fragments

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

30. Priming DNA DNA polymerases can only add nucleotides to an existing strand A RNA primer, first binds to the template strand with the help of primase (aka RNA Polymerase) Eventually replaced by DNA molecules

31. Primer continued... The leading strand requires only one primer For the lagging strand, each fragment requires a new primer The primer is replaced by DNA polymerase

33. DNA Polymerase – An Amazing Enzyme DNA pol proofreads each nucleotide that it adds against the template If an error is made, the enzyme deletes the nucleotide and continues synthesizing DNA Other proteins do the same thing DNA is also repaired after damage, such as exposure to X-rays Over 100 DNA repair enzymes! Extremely, extremely important

34. DNA Repair/ Excision Repair Nucleases cut out (incise) the incorrect nucleotide DNA polymerase adds the correct nucleotide Ligase connects the new nucleotide to the strand

35. Topoisomerase Helicase Single Stranded Binding Proteins

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