DNA was identified as the genetic material through

DNA was identified as the genetic material through a series of experiments

Molecular Genetics l Study of the chemistry of the materials of inheritance. Structure of DNA l Contains information to construct the molecules needed for life (proteins). l

Griffith and Transformation l 1928 Frederick Griffith was researching pneumonia.

Griffith finds a ‘transforming principle. ’ l Griffith experimented with the bacteria that causes pneumonia. l Two types: 1. S = deadly (Sick) 2. R = harmless l TRANSFORMATION occurred l S changed R into harmful

Griffith’s Experiment Heat killed disease causing bacteria Disease causing bacteria Harmless Bacteria Heat Killed bacteria No growth Harmless bacteria MOUSE CROAKS!

Transformation l Griffith mixes heat-killed disease causing bacteria with live harmless bacteria l The mice died l A factor from the heat killed bacteria had “transformed” *(CHANGED) the harmless bacteria into disease causing ones.

Griffith’s Experiment l Experiment Video

Avery and DNA Oswald Avery – 1944 l Repeats Griffith’s experiment l Wants to know what caused the transformation? l Uses enzymes to break down or destroy parts of the pneumonia causing bacteria l

Avery and DNA Parts of Bacteria Proteins RNA Did transformation occur afterwards? Conclusion

Avery's Experiment l Enzyme l Transformation occurred- l Enzyme l to break down RNA Transformation occurred l Enzyme l to break down proteins to break down DNA NO TRANSFORMATION OCCURRED

Avery and DNA l Conclusion: l DNA caused transformation! l If is causes transformation then: l Could DNA be genetic material?

The Hershey-Chase Experiment Alfred Hershey and Martha Chase -1952 l Studied viruses l l l non-living particles smaller than a cell can infect living organisms

1952 Alfred Hershey and Martha Chase l Is genetic material made of DNA or Protein? l Used radioactive sulfur 35 and phosphorus 32 l Bacteriophage

The Hershey-Chase Experiment l Bacteriophage – a virus that infects and kills bacteria (bacteria eater) l Composed of: DNA or RNA core l protein coat l

The Hershey-Chase Experiment Bacteriophage with phosphorus-32 in DNA Bacteriophage with sulfur-35 in protein coat Phage infects bacterium Radioactivity inside bacterium No radioactivity inside bacterium

The Hershey-Chase Experiment l Video

The Hershey-Chase Experiment l Conclusion: The genetic material is DNA

Francis Crick and James Watson 1953 Developed a 3 -D model of DNA l Used information from other scientists l Two strands are wound around each other l Looks like: l Twisted ladder l Spiral staircase l

Erwin Chargaff’s Rules 1950 Erwin Chargaff – American Biochemist l In any sample of DNA l l l Percentages of cytosine and guanine are almost equal Percentages of thymine and adenine are almost equal l C=G and T=A Percentages of Bases in Four Organisms Sources of DNA Streptococcus Yeast Herring Human A 29. 8 31. 3 27. 8 30. 9 T 31. 6 32. 9 27. 5 29. 4 G 20. 5 18. 7 22. 2 19. 9 C 18. 0 17. 1 22. 6 19. 9

X-Ray Evidence Early 1950’s l Rosalind Franklin used x-ray on DNA l X-shaped pattern suggests - two strands in the structure l

Francis Crick and James Watson 1953 DNA is shaped as a double helix. l Two strands are wound around each other l Looks like: l Twisted ladder l Spiral staircase l