Explain 'Transforming Principle' in Griffith experiment,'S strain and R strain' in griffith experiment?

Transforming Principle

  • Griffith performed experiments with the bacteria Streptococcus pneumoniae. This bacterium has two strains − S strain and R strain.

S strain Bacteria

R strain Bacteria

  • Produce smooth colonies on culture plate

  • Produce rough colonies on culture plate

  • Have a polysaccharide coat

  • Do not have a polysaccharide coat

  • Virulent (causes pneumonia)

  • Non-virulent (does not cause pneumonia)

  • Griffith’s experiment

  • Live R strain in the presence of heat-killed S strain produce virulence because somehow R strain bacteria is transformed by heat-killed S strain bacteria. Hence, it was concluded that there must be transfer of genetic material.

Biochemical Nature of Transforming Material

  • Avery, McLeod, and McCarthy worked to determine the biochemical nature of genetic material responsible for transformation.

  • This suggests that DNA has to be the genetic material.

R strain of Streptococcus pneumonia is not virulent as it does not produce polysaccharide coat (virulence factor).

S strain of Streptococcus pneumonia is virulent due to the presence of polysaccharide capsule

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