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

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

Griffith and Transformation 1928 Frederick Griffith was researching pneumonia.

Griffith finds a ‘transforming principle.’ Griffith experimented with the bacteria that causes pneumonia. Two types: S = deadly (Sick) R = harmless TRANSFORMATION occurred 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 Griffith mixes heat-killed disease causing bacteria with live harmless bacteria The mice died A factor from the heat killed bacteria had “transformed” *(CHANGED) the harmless bacteria into disease causing ones.

Griffith’s Experiment Experiment Video

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

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

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

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

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

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

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

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

The Hershey-Chase Experiment Video

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

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

Erwin Chargaff’s Rules 1950 Erwin Chargaff – American Biochemist In any sample of DNA Percentages of cytosine and guanine are almost equal Percentages of thymine and adenine are almost equal C=G and T=A Percentages of Bases in Four Organisms Sources of DNA A T G C Streptococcus 29.8 31.6 20.5 18.0 Yeast 31.3 32.9 18.7 17.1 Herring 27.8 27.5 22.2 22.6 Human 30.9 29.4 19.9

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

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