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1. Transforming principle
(Griffith’s Experiment)
DNA- a genetic material
By-Dr R K Upadhyay
PGT, Biology

2. Frederick Griffith
• 1928
• Mice
• Virulent strain of pneumonia
(S strain)
• Non virulent strain of
Pneumonia (R strain)
• Streptococcus pneumoniae)

3. ‘S’ and ‘R’ strain
• Type III-S (smooth) – virulent
• Type II-R (rough)- nonvirulent.
• The III-S strain synthesize a polysaccharide capsule that
protected itself from the host's immune system, resulting
in the death of the host’
• While the II-R strain don’t have that protective capsule and
was defeated by the host's immune system

4. Transformation
• bacteria are capable of transferring genetic
information through a process known as
transformation

5. Griffith experiment
• MICE + S strain------mice died due to Pneumonia
• MICE + R strain------mice alive

6. Griffith experiment
• MICE + heat killed S strain------mice live
• MICE + heat killed S strain + R strain------mice
died due to Pneumonia.

7. Reason
• Due to transformation the genetic material from heat killed
‘S’ strain transferred to the ‘R’ strain.
• ‘R’ strain (non virulent) transformed into ‘S’ strain (virunet)

9. Biochemical characterization of transforming principle
• Oswald Avery, Colin MacLeod, and Maclyn McCarty
• Prove DNA is genetic material.

10. Use of enzymes Protease, Rnase, DNase
• MICE + heat killed S strain + R strain +
Protease mice died
• MICE + heat killed S strain + R strain +
RNase mice died
• MICE + heat killed S strain + R strain +
Protease mice died

11. Conclusion
• There is no effect of Proteins and RNA on the
virulent property of Bacteria.
• DNA has virulent property.