The Avery and Hershey-Chase Experiments:

1
The Avery and Hershey-Chase Experiments

• The Active Principle is DNA!

LeAnne, Carly, and Drabe.
2
The Avery Experiments

• Avery provided conclusive evidence that DNA is
  the heredity material for the bacterial specimens
  under investigation.
• Oswald Avery (with his co-workers MacLeod and
  McCarty) characterized what they called the
  transforming principle from Griffiths
  experiment.
• They prepared a mixture of dead S Streptococcus
  and live R Streptococcus. (That Griffith had
  used).
• Avery and his colleagues achieved 99.98 purity
  by removing as they could form their mixtures.
• The transforming activity was NOT reduced.

3
Avery Experiments (cont.)

• The properties of the transforming principle
  resembled those of DNA in several ways
• When the purified principle was analyzed
  chemically, the array of elements agreed closely
  with DNA
• When spun at high speeds, the transforming
  principle migrated at the same level (density) as
  DNA
• Extracting the lipid and protein from the
  purified transforming principle did not reduce
  its activity
• Protein-digesting enzymes did not affect the
  principles activity, nor did RNA-digesting
  enzymes
• The DNA-digesting enzyme DNase destroyed all
  transforming activity

4
Avery Experiment Conclusion

• The researchers concluded that a nucleic acid of
  the deoxyribose type is the fundamental unit of
  the transforming principle of Pneumococcus Type
  III basically
• DNA is the hereditary material for this bacterial
  species.

5
The Hershey-Chase Experiment

• Hershey and Chase provided further evidence that
  heredity material in bacteriophages was found in
  DNA, not in proteins.
• Many did not accept Averys conclusions until
  1952 when Alfred Hershey and Martha Chase
  conducted this experiment with bacteriophages
  (viruses that attack bacteria)

6
The Hershey Chase Experiment

• In the Hershey-Chase experiment, bacterial
  viruses called phage, were used to demonstrate
  that DNA is the genetic material. The phage used
  in this experiment consisted of a DNA molecule
  surrounded by a protein coat.
• When phage infect bacteria, they attach to the
  surface of the bacterium and inject the DNA into
  the cell. The protein coat remains on the outside
  of the cell.

7
Hershey-Chase (cont.)

• In the first part of the experiment, phage were
  produced in a medium containing S-35
  radioactively labeled amino acids. This resulted
  in a phage population with S-35 labeled proteins
  but no radioactive label in the DNA
• The phage were then allowed to infect the
  bacteria.
• They attached to the bacterial cell and injected
  their DNA, but the radioactively-labeled protein
  coat remained on the outside of the cell

8
Hershey-Chase (cont.)

• The phage produced in these cells contained no
  radioactivity.
• Vigorous shaking caused the empty protein coats
  to be removed, but did not interfere with
  production of new phage.
• In the second part, phage were produced in a
  medium containing P-32 labeled deoxyribonucleotide
  s. This resulted in phage population with P-32
  labeled DNA, but no radioactive label in the
  protein.

9
Hershey-Chase (cont.)

• When the phage infected the bacteria, the P-32
  labeled DNA entered the cell and could not be
  found in phage subsequently produced in the
  infected bacteria.
• This demonstrated that the DNA, but not the
  protein, carries the genetic information for a
  new generation of phage! SWEET!