1. Its History, Structure and Function DNA

2. Johann Friedrich Miescher Isolated DNA from leukocytes Called it “nuclein” WHO DISCOVERED DNA?

3. MEI MIESCHER’S WORK Late 1800s Disproved that the nucleus is mostly protein Isolated the components of DNA: mostly carbon, hydrogen, oxygen, nitrogen, and phosphorus No known proteins had that much phosphorus (3%)

4. Frederick Griffith (1928) Worked with bacteria “Transformed” non- infectious bacteria into virulent bacteria Called the part that controlled virulence a “transforming principle” WAS DNA THE MOLECULE OF HEREDITY?

5. GRIFFITH’S EXPERIMENT

6. AVERY AND MACLEOD (1944)

7. THEIR EXPERIMENT

8. CONCLUSIONS A chemical is responsible for the virulence of Pneumococcus bacteria The chemical was not a protein, a lipid, a carbohydrate, or RNA The chemical was DNA

9. HERSHEY AND CHASE (1952)

10. THEIR EXPERIMENT

11. CONCLUSIONS The active component of the bacteriophage that transmits the infective characteristic is the DNA. There is a clear correlation between DNA and genetic information. Source: Access Excellence

12. WHAT IS DNA’S STRUCTURE? Erwin Chargaff (1952) Maurice Wilkins and Rosalind Franklin (1953) J.D. Watson and Francis Crick (1953)

13. In nuclear DNA: % A = % T % C = % G Led to idea of complementary base pairing CHARGAFF’S RULE

14. WILKINS, FRANKLIN, AND PHOTO 51

15. PHOTO 51

16. WATSON AND CRICK

17. WHAT IS THE STRUCTURE OF DNA? Double helix Two “backbones”: alternating deoxyribose and phosphate groups Twisted “ladder”: the “rungs” are the paired nitrogenous bases Antiparallel Strands run in opposite directions

18. WHAT IS THE STRUCTURE OF DNA? Complementary base pairing A pairs with T, C with G Hydrogen bonding between bases Two bonds between A & T; three between C & G Easily broken, easily reformed

19. THE DOUBLE HELIX

20. NUCLEOTIDE STRUCTURE

21. FIVE NUCLEOTIDES

22. STEPS IN REPLICATION Helicase unwinds the double helix, forming replication forks DNA polymerase III binds free nucleotides to the exposed complementary bases Replication occurs in the 5‘ to 3‘ direction (lead strand and lag strand); bases can only be added to the 3’ end of the growing DNA molecule Other enzymes correct errors, remove primers, seal “nicks” in the backbone The resulting daughter DNA molecules each consist of an original strand and a new strand

23. PROKARYOTE ORIGIN OF REPLICATION

24. EUKARYOTE ORIGIN OF REPLICATION