Table of Contents
- 1 What happened when Griffith injected the mice with the harmless R strain bacteria alone?
- 2 What happened when Griffith injected the R strain bacteria into the healthy mouse?
- 3 What happened to the mice when injected with harmless bacteria in Griffith’s experiments when injected with the harmful bacteria?
- 4 How did Griffith determine which strain caused disease?
- 5 What happened when Griffith injected mice with the pneumonia causing strain of bacteria?
- 6 What was the essential conclusion of Griffith’s experiment on bacteria and mice?
- 7 What happened when Griffith injected mice with living are bacteria and dead S bacteria?
What happened when Griffith injected the mice with the harmless R strain bacteria alone?
The experiments took an unexpected turn, however, when harmless R bacteria were combined with harmless heat-killed S bacteria and injected into a mouse. Not only did the mouse develop pnenumonia and die, but when Griffith took a blood sample from the dead mouse, he found that it contained living S bacteria!
What happened when Griffith injected the R strain bacteria into the healthy mouse?
In the critical experiment, Frederick Griffith (1928) mixed heat-killed S with live R and injected the combination into mice: the mouse died. The dead mouse’s tissues were found to contain live bacteria with smooth coats like S.
What happened to the mice when injected with harmless bacteria in Griffith’s experiments when injected with the harmful bacteria?
Experiment 4: Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria and injected the mixture into the mice. The mice developed pneumonia and died.
What happened to the R strain bacteria?
Even without the S-strain proteins, the R-strain was changed, or transformed, into the deadly strain. However, when the researchers inactivated DNA in the S-strain, the R-strain remained harmless. This led to the conclusion that DNA is the substance that controls the characteristics of organisms.
Why did Griffith inject a mouse with live harmless bacteria?
When Griffith injected mice with disease-causing bacteria, the mice developed pneumonia and died. When he injected mice with harmless bacteria, the mice stayed healthy.
How did Griffith determine which strain caused disease?
Upon isolating the live bacteria from the dead mouse, only the S strain of bacteria was recovered. When this isolated S strain was injected into fresh mice, the mice died. Griffith concluded that something had passed from the heat-killed S strain into the live R strain and transformed it into the pathogenic S strain.
What happened when Griffith injected mice with the pneumonia causing strain of bacteria?
The disease-causing bacteria (S strain) grew into smooth colonies on culture plates, whereas the harmless bacteria (R strain) produced colonies with rough edges. When Griffith injected mice with disease-causing bacteria, the mice developed pneumonia and died.
What was the essential conclusion of Griffith’s experiment on bacteria and mice?
Griffith concluded that the R-strain bacteria must have taken up what he called a “transforming principle” from the heat-killed S bacteria, which allowed them to “transform” into smooth-coated bacteria and become virulent.
What did Avery conclude from his experiments?
Avery and his colleagues concluded that protein could not be the transforming factor. Next, they treated the mixture with DNA-destroying enzymes. This time the colonies failed to transform. Avery concluded that DNA is the genetic material of the cell.
What did Griffith think that could be the transforming factor that changed a harmless bacteria into a harmful one?
Griffith reasoned that some chemical factor that could change harmless bacteria into disease-causing bacteria was transferred from the heat-killed cells of the S strain into the live cells of the R strain. He called this process transformation, because one type of bacteria had been changed permanently into another.