Question

1.) Briefly explain the general procedure and purpose of the Griffth Transformation experiement.

2.) If Avery, Macleod, and McCarty had found that samples of heat-killed bacteria treated with RNase and DNase transformed bacteria, but samples treated with protease did not, what conclusion would they have made?

Answer 1

Answer 1:

Griffith carried out transformation experiment with the purpose of ​​​​​demonstrating that genetic material can be passed from one bacteria to another. The process by which bacteria take up genes from external environment is called transformation.

Background information:

Griffith used two different strains of Streptococcus pneumoniae ​​​​​:

(1) virulent smooth strain (III S)

(2) non virulent, rough strain (II R)

S strain is virulent due to the presence of a polysaccharide capsule. When injected, it can multiply within mice and lead to pneumonia and death of mice.

R strain lacks the capsule layer and when injected into mice, gets eliminated by the immune system of mice. It cannot lead to development of pneumonia and mice survives.

Procedure:

1. Griffith injected live non virulent R strain into mice. The mice survived.
2. Griffith injected live virulent S strain into mice. The mice developed pneumonia and died.
3. Griffith injected heat killed S strain into mice and couldn't induce pneumonia. Mice could survive.
4. Finally, he injected a mixture of heat killed S type and live R type bacteria into mice. The mice developed pneumonia and died.

Live IIR-strain (Non-virulent, non-capsulated) Injected into mouse Mouse survives Live IIIS-strain (Virulent, capsulated) Injected into mouse Mouse dies Heat killed IIIS-strain Injected into mouse Mouse survives Heat killed IIIS-strain and live IIR-strain Injected into mouse Mouse dies Results of Griffith's experiment

Conclusion:

R type bacteria acquired genes for virulence factors (genetic material) from heat killed S type bacteria and itself got transformed into virulent form. This developed pneumonia in the mice, and mice couldn't survive.

Answer 2:

If Avery, Macleod, and McCarty had found that samples of heat-killed bacteria treated with RNase and DNase transformed bacteria, but samples treated with protease did not then it could have been concluded that the genetic material is protein.

Explanation:

Application of protease degrades proteins. Such a degraded protein is non-functional and if it were the genetic material, then it couldn't have been able to transform the R strain into S strain.

DNase degrades DNA and RNase degrades RNA. Cells treated with these two enzymes won't affect proteins, and it could result into transformation. (Considering proteins to be genetic material).

Note : In actual experiment, cells treated with DNase couldn't carry out transformation, and DNA was shown to be the genetic material.

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