What was the scientific conclusion of Frederick Griffith's experiments with Streptococcus pneumoniae?

• A. The formulation of the central dogma of molecular biology
• B. The development of the polymerase chain reaction ($\mathrm{PCR}$)
• C. The identification of $\mathrm{DNA}$ as the transforming principle
• D. The discovery of the double helix structure of $\mathrm{DNA}$

Answer: (C)

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1. Frederick Griffith's experiments involved two strains of Streptococcus pneumoniae: a virulent smooth strain (S) with a polysaccharide capsule and a non-virulent rough strain (R) without the capsule.
2. Griffith observed that when he injected mice with the live R strain and heat-killed S strain, the mice developed pneumonia and died, and live S strain bacteria were found in their bodies.
3. This suggested that some 'transforming principle' from the heat-killed S strain was taken up by the R strain, converting it into the virulent S strain.
4. Griffith's conclusion was that this 'transforming principle' was responsible for transferring genetic information, although he did not identify it as DNA.
5. Later experiments by Avery, MacLeod, and McCarty identified DNA as the 'transforming principle,' confirming Griffith's findings and establishing DNA as the molecule responsible for heredity.