DNA The Genetic Material

1. DNA The Genetic Material

2. Scientific History • The march to understanding that DNA is the genetic material • T.H. Morgan (1908) • Frederick Griffith (1928) • Avery, McCarty & MacLeod (1944) • Erwin Chargaff (1947) • Hershey & Chase (1952) • Watson & Crick (1953) • Meselson & Stahl (1958)

3. 1908 | 1933 Chromosomes related to phenotype • T.H. Morgan • working with Drosophila • fruit flies • associated phenotype with specific chromosome • white-eyed male had specific X chromosome

4. 1908 | 1933 Genes are on chromosomes • Morgan’s conclusions • ________________________ • but is it the protein or the DNA of the chromosomes that are the genes? • initially proteins were thought to be genetic material… Why? What’s so impressiveabout proteins?!

5. 1928 The “Transforming Principle” • Frederick Griffith • Streptococcus pneumonia bacteria • was working to find cure for pneumonia • harmless live bacteria (“rough”) mixed with heat-killed pathogenic bacteria (“smooth”) causes fatal disease in mice • a substance passed from dead bacteria to live bacteria to change their phenotype • _____________________________

6. The “Transforming Principle” mix heat-killed pathogenic & non-pathogenic bacteria live pathogenic strain of bacteria live non-pathogenic strain of bacteria heat-killed pathogenicbacteria A. B. D. C. mice die mice live mice live mice die Transformation=change in phenotype something in heat-killed bacteria could still transmit disease-causing properties

7. 1944 DNA is the “Transforming Principle” • Avery, McCarty & MacLeod • purified both DNA & proteins separately from Streptococcus pneumonia bacteria • which will transform non-pathogenic bacteria? • injected protein into bacteria • no effect • injected DNA into bacteria • transformed harmless bacteria into virulent bacteria mice die What’s the conclusion?

8. 1944 | ??!! Avery, McCarty & MacLeod • Conclusion • ______________________________________________________________________________________ Oswald Avery Maclyn McCarty Colin MacLeod

9. 1952 | 1969 Hershey Confirmation of DNA • Hershey & Chase • classic “blender” experiment • worked with bacteriophage • viruses that infect bacteria • grew phage viruses in 2 media, radioactively labeled with either • ____________________ • ____________________ • infected bacteria with labeled phages Why useSulfurvs.Phosphorus?

10. Protein coat labeled with 35S DNA labeled with 32P Hershey & Chase T2 bacteriophages are labeled with radioactive isotopes S vs. P bacteriophages infect bacterial cells bacterial cells are agitated to remove viral protein coats Which radioactive marker is found inside the cell? Which molecule carries viral genetic info? 32P radioactivity foundin the bacterial cells 35S radioactivity found in the medium

12. Blender experiment • Radioactive phage & bacteria in blender • ___________________ • radioactive proteins stayed in supernatant • therefore viral protein did NOT enter bacteria • ___________________ • radioactive DNA stayed in pellet • therefore viral DNA did enter bacteria • ___________________________________ Taaa-Daaa!

13. 1952 | 1969 Hershey Hershey & Chase Martha Chase Alfred Hershey

14. 1947 Chargaff • DNA composition: “________________” • varies from species to species • all 4 bases not in equal quantity • bases present in characteristic ratio • humans: A = 30.9% T = 29.4% G = 19.9% C = 19.8% RulesA = T C = G That’s interesting!What do you notice?

15. 1953 | 1962 Structure of DNA • Watson & Crick • ___________________________________ • other leading scientists working on question: • Rosalind Franklin • Maurice Wilkins • Linus Pauling Wilkins Pauling Franklin

16. 1953 article in Nature Watson and Crick Watson Crick

17. Rosalind Franklin (1920-1958)

18. But how is DNA copied? • Replication of DNA • base pairing suggests that it will allow each side to serve as a template for a new strand “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” —Watson & Crick

19. Can you designa nifty experimentto verify? Models of DNA Replication • Alternative models • become experimental predictions semiconservative semiconservative semiconservative P 1 2

20. 1958 Semiconservative replication • Meselson & Stahl • label “parent” nucleotides in DNA strands with heavy nitrogen =15N • label new nucleotides with lighter isotope = 14N “The Most Beautiful Experiment in Biology” Make predictions… parent replication 15N/15N 15N parent strands

21. 15N/15N 15N parent strands Predictions ________ 1st round of replication ________ ________ ________ semi-conservative conservative dispersive 2nd round of replication ________ ________ P ________ ________ ________ 1 semi-conservative conservative dispersive 2

22. Meselson & Stahl Matthew Meselson Franklin Stahl Franklin Stahl Matthew Meselson

23. Scientific History • March to understanding that DNA is the genetic material • T.H. Morgan (1908) • ___________________________________________________ • Frederick Griffith (1928) • ___________________________________________________ • Avery, McCarty & MacLeod (1944) • ___________________________________________________ • Erwin Chargaff (1947) • ___________________________________________________ • Hershey & Chase (1952) • ___________________________________________________ • Watson & Crick (1953) • ___________________________________________________ • Meselson & Stahl (1958) • ___________________________________________________

24. The “Central Dogma” • Flow of genetic information in a cell translation translation DNA RNA protein replication

25. Science …. Fun Party Time! Any Questions??