Question
14. Griffith investigated how certain types of bacteria produce pneumonia in mice, explain this experiment.
Answers
GPT-4o mini
The experiment conducted by Frederick Griffith in 1928 is a classic study in microbiology that demonstrated the phenomenon of transformation in bacteria. Griffith was investigating two strains of the bacterium *Streptococcus pneumoniae,* which causes pneumonia. The two strains he studied were:
1. **S strain (smooth strain)**: This strain had a smooth capsule that protected it from the mouse's immune system, making it virulent (capable of causing disease).
2. **R strain (rough strain)**: This strain did not have a capsule and was thus non-virulent (not capable of causing disease).
Griffith's experiment involved several key steps:
1. **Injection of Mice with S Strain**: He injected one group of mice with the live S strain bacteria. As expected, these mice developed pneumonia and died.
2. **Injection of Mice with R Strain**: He injected another group of mice with live R strain bacteria. These mice did not develop pneumonia and remained healthy.
3. **Heated S Strain**: Griffith then injected a third group of mice with heat-killed S strain bacteria. Since the bacteria were killed by heat, these mice also remained healthy.
4. **Mixture of S and R Strains**: In a crucial step, he mixed live R strain bacteria with heat-killed S strain bacteria and injected this mixture into a fourth group of mice. Surprisingly, these mice developed pneumonia and died.
5. **Isolation of Bacteria**: After the death of the mice, Griffith was able to isolate live S strain bacteria from their bodies. This indicated that something from the dead S strain bacteria had transformed the live R strain bacteria into virulent S strain bacteria.
Through this experiment, Griffith concluded that the R strain bacteria had taken up some "transforming principle" from the dead S strain bacteria, which enabled them to produce the smooth capsule and become virulent. This provided early evidence for the concept of genetic transformation, laying the groundwork for future discoveries about DNA as the carrier of genetic information.
1. **S strain (smooth strain)**: This strain had a smooth capsule that protected it from the mouse's immune system, making it virulent (capable of causing disease).
2. **R strain (rough strain)**: This strain did not have a capsule and was thus non-virulent (not capable of causing disease).
Griffith's experiment involved several key steps:
1. **Injection of Mice with S Strain**: He injected one group of mice with the live S strain bacteria. As expected, these mice developed pneumonia and died.
2. **Injection of Mice with R Strain**: He injected another group of mice with live R strain bacteria. These mice did not develop pneumonia and remained healthy.
3. **Heated S Strain**: Griffith then injected a third group of mice with heat-killed S strain bacteria. Since the bacteria were killed by heat, these mice also remained healthy.
4. **Mixture of S and R Strains**: In a crucial step, he mixed live R strain bacteria with heat-killed S strain bacteria and injected this mixture into a fourth group of mice. Surprisingly, these mice developed pneumonia and died.
5. **Isolation of Bacteria**: After the death of the mice, Griffith was able to isolate live S strain bacteria from their bodies. This indicated that something from the dead S strain bacteria had transformed the live R strain bacteria into virulent S strain bacteria.
Through this experiment, Griffith concluded that the R strain bacteria had taken up some "transforming principle" from the dead S strain bacteria, which enabled them to produce the smooth capsule and become virulent. This provided early evidence for the concept of genetic transformation, laying the groundwork for future discoveries about DNA as the carrier of genetic information.