12 Questions
What is the name of the bacterium that causes pneumonia with a smooth coating made of carbohydrates?
S form
What happened when Griffith injected mice with only the heat-killed S bacteria?
Mice were unaffected
What did Griffith discover when he injected mice with a combination of heat-killed S bacteria and live R bacteria?
The mice died
What was the significance of finding live S bacteria in blood samples from the dead mice injected with a combination of heat-killed S bacteria and live R bacteria?
It indicated a transfer of material from heat-killed S bacteria to live R bacteria
What did Griffith conclude about the material transferred from heat-killed S bacteria to live R bacteria?
It changed harmless R bacteria into disease-causing S bacteria
"What did Oswald Avery and his fellow biologists work on for more than ten years after Griffith's discovery of the transforming principle?"
"Finding out what exactly the transforming principle was"
What did Avery's group observe directly in a petri dish?
Transformation of R bacteria into S bacteria
What did the standard chemical tests reveal about the transforming principle?
DNA was present
What element's presence in the extract supported the hypothesis that DNA was the transforming principle?
Phosphorus
What happened when enzymes known to break down proteins were added to the extract?
The extract still transformed R bacteria to S form
What did some scientists question despite Avery's evidence?
The genetic material in bacteria compared to other organisms
Why did some scientists insist that Avery's extract must have contained protein?
Despite DNA presence, protein may have played a role
Study Notes
Pneumonia-Causing Bacterium
- The bacterium that causes pneumonia has a smooth coating made of carbohydrates, known as the S bacteria.
Griffith's Experiment
- When Griffith injected mice with only heat-killed S bacteria, nothing happened, and the mice did not die.
- However, when Griffith injected mice with a combination of heat-killed S bacteria and live R bacteria, the mice died.
- Griffith discovered that the live R bacteria had transformed into the deadly S bacteria, causing the mice to die.
Significance of Griffith's Discovery
- The finding of live S bacteria in blood samples from the dead mice injected with a combination of heat-killed S bacteria and live R bacteria showed that the R bacteria had transformed into the S bacteria.
- This transformation implied that some material was transferred from the heat-killed S bacteria to the live R bacteria.
Griffith's Conclusion
- Griffith concluded that the material transferred from heat-killed S bacteria to live R bacteria was a "transforming principle" that allowed the R bacteria to change into the deadly S bacteria.
Avery's Research
- Oswald Avery and his fellow biologists worked on isolating the transforming principle for over ten years after Griffith's discovery.
- Avery's group observed that the transforming principle was able to transform R bacteria into S bacteria in a petri dish.
Properties of the Transforming Principle
- Standard chemical tests revealed that the transforming principle was resistant to protein-destroying enzymes and was not affected by lipid solvents.
- The presence of phosphorus in the extract supported the hypothesis that DNA was the transforming principle.
- When enzymes known to break down proteins were added to the extract, the transforming principle was not affected.
Skepticism of Avery's Findings
- Some scientists questioned Avery's evidence, despite the strong results, suggesting that the extract must have contained protein.
- This skepticism was due to the prevailing belief at the time that proteins were the genetic material, rather than DNA.
Learn about Frederick Griffith's groundbreaking experiment in 1928 involving two forms of bacteria that led to the discovery of a 'transforming principle'. Understand the significance of S and R forms of the bacterium in causing pneumonia.
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