Lecture Notes on Frederick Griffith's Experiment

Introduction to Frederick Griffith

• Pioneer in demonstrating bacterial transformation.
• Conducted experiments in 1928 while seeking a pneumonia vaccine.
• Pneumonia was often deadly in the past, even in healthy individuals.

Background on Streptococcus pneumoniae

• Bacteria exists in several strains:
  • Virulent S strain: Smooth polysaccharide coat, protects from immune system.
  • Non-virulent R strain: Rough coat, does not cause disease.

Key Observations

• Griffith noticed the R strain could sometimes revert to the S strain.
• He theorized about a transforming principle between the strains.

Experimental Design

• Griffith injected five types of bacteria into groups of mice:
  1. Live R strain
  2. Live S strain
  3. Heat-killed S strain
  4. Combination of heat-killed S strain and live R strain
  5. S strain isolated from mice in the fourth group

Results of the Experiment

• Group 1: Mice injected with live R strain survived.
• Group 2: Mice injected with live S strain developed pneumonia and died.
• Group 3: Mice injected with heat-killed S strain survived (dead bacteria).
• Group 4: Mice injected with heat-killed S strain + live R strain developed pneumonia and died.
  • Conclusion: Live R strain acquired dangerous properties from the dead S strain (transformation).
• Group 5: Mice injected with isolated S strain from Group 4 developed pneumonia and died.

Conclusion of Griffith's Findings

• Identified the transformation principle as the component enabling R strain to become virulent.
• Exact nature of the transforming principle remained unknown at the time.
• Significant findings regarding non-heritable exchange of genetic information.

Further Developments

• 1944: Avery, MacLeod, and McCarty confirmed nucleic acids (not proteins) are hereditary molecules.
• Griffith's work laid the foundation for future genetics research.

Additional Resources

• Questions can be directed to the comment section.
• Study guide linked in the video description for further reference.
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