Griffith's experiment

Summary

In 1928, Griffith conducted a groundbreaking experiment on Streptococcus pneumoniae, observing two strains: the smooth, highly pathogenic strain with a protective capsule, and the rough, less pathogenic strain without it. When heat-killed smooth strain was mixed with live rough strain and injected into mice, the mice died, indicating a 'transforming principle' was transferred, converting the rough strain into a pathogenic form. Griffith's experiment laid the foundation for understanding genetic transformation, later identified as DNA by Avery, MacLeod, and McCarty.

Takeaways

• 🧬 Griffith's experiment in 1928 focused on the bacterium Streptococcus pneumoniae, which has two strains: smooth and rough.
• 🛡️ The smooth strain of S. pneumoniae is highly pathogenic due to a protective capsule that shields it from the immune system.
• 🔬 The rough strain lacks the capsule, making it less pathogenic and more easily destroyed by the immune system.
• 🐁 When injected into mice, the smooth strain kills the mice, while the rough strain does not.
• 🔥 Griffith found that heat-killed smooth strain bacteria did not kill mice when injected, indicating the capsule's role in pathogenicity.
• 🤔 When heat-killed smooth strain was mixed with live rough strain and injected, the mice died, suggesting a 'transforming principle' was transferred.
• 🧐 Griffith did not identify the transforming principle, but subsequent experiments by Avery, MacLeod, and McCarty revealed it to be DNA.
• 🔍 The experiment demonstrated that DNA from the heat-killed smooth strain could transform the rough strain into a smooth, highly pathogenic strain.
• 🌟 This was a groundbreaking discovery, as it was the first evidence that DNA carried genetic information and could induce heritable changes in bacteria.
• 🎶 The script concludes with a musical note, possibly indicating a summary or transition to another topic.

Q & A

Who was Griffith and what was his significant discovery in 1928?

Frederick Griffith was a British bacteriologist who, in 1928, discovered the phenomenon of transformation in bacteria. He found that a non-virulent strain of Streptococcus pneumoniae could become virulent after being exposed to heat-killed virulent strains.

What are the two types of Streptococcus pneumoniae strains mentioned in the script?

The two types of Streptococcus pneumoniae strains mentioned are the smooth strain and the rough strain. The smooth strain has a protective capsule that makes it highly pathogenic, while the rough strain lacks this capsule and is less virulent.

What is the role of the capsule in the smooth strain of Streptococcus pneumoniae?

The capsule in the smooth strain of Streptococcus pneumoniae serves as a protective layer that shields the bacteria from the host's immune system, thereby making it highly pathogenic and able to cause disease.

Why does the rough strain of Streptococcus pneumoniae not cause disease when injected into mice?

The rough strain of Streptococcus pneumoniae does not cause disease when injected into mice because it lacks the protective capsule. As a result, the immune system can easily recognize and eliminate these bacteria.

What was the surprising result of Griffith's experiment when heat-killed smooth strain bacteria were mixed with the rough strain?

The surprising result was that when heat-killed smooth strain bacteria were mixed with the rough strain and injected into mice, the mice died. This indicated that some 'transforming principle' was transferred from the dead smooth strain to the rough strain, making it pathogenic.

What is the term used to describe the phenomenon where the rough strain becomes pathogenic after exposure to heat-killed smooth strain?

The phenomenon where the rough strain of Streptococcus pneumoniae becomes pathogenic after exposure to heat-killed smooth strain is known as the 'transforming principle.'

Who were Avery, MacLeod, and McCarty, and what did they contribute to the understanding of the transforming principle?

Oswald Avery, Colin MacLeod, and Maclyn McCarty were scientists who, through their experiments, identified DNA as the transforming principle. They showed that DNA from the heat-killed smooth strain could transform the rough strain into a pathogenic form.

How did Avery, MacLeod, and McCarty prove that DNA was the transforming principle?

Avery, MacLeod, and McCarty proved that DNA was the transforming principle by demonstrating that a purified DNA preparation from the heat-killed smooth strain could induce the transformation in the rough strain, converting it into a smooth, pathogenic strain.

What was Griffith's limitation in understanding the nature of the transforming principle?

Griffith's limitation was that he did not identify the chemical nature of the transforming principle. He observed the phenomenon of transformation but did not determine that DNA was the substance responsible for the change in virulence.

What is the significance of the Griffith experiment in the field of genetics?

The Griffith experiment is significant in genetics because it was the first demonstration of genetic transformation in bacteria, laying the groundwork for understanding how genetic material can be transferred between organisms and leading to the discovery of DNA's role in heredity.