DNA L14 (Evidence)

Evidence for DNA as Genetic Material

Chromosomes have

DNA & proteins (20 amino acids)

Frederick Griffith (1982)

Bacteriologist & embryologis

working on a pneumonia vaccine

1st to show evidence against protein hypothesis

2 Strains

• rough: non pathogenic strain

• smooth: causes pneumonia

Transformation- change in genotype or phenotype due to assimilation of eternal DNA

• characteristic of the rough strain was transformed & causes the mouse to die

Aver, MacLeod & McCarty

1. Lysed S cells

2. Separated contents into: lipids, proteins, polysaccharides & nucleic acids

3. Tested each for transforming ability

4. Only DNA could transform

Hershey & Chase

Bacteriophages (phages)

• viruses that affect bacteria

• virus is just DNA (or RNA) and a protein shell

• Grow 1 virus population with radioactive sulfur & the the other with radioactive phosphorus

• Allowed each to infect bacteria

• Separate Viruses from bacteria

• Conclusion- injected DNA of Phage is the genetic information

Summary of Evidence for DNA as Genetic MAterial

Griffith: Transformation

Avery Macleod & McCarty: DNA is a transforming material

Hershey & Chase: Virus DNA contains genes