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In: Biology

In some critical experiments, Avery, MacLeod and McCarty confirmed an important principle, essentially identifying DNA as...

In some critical experiments, Avery, MacLeod and McCarty confirmed an important principle, essentially identifying DNA as the genetic material. Their experiments used rough (R) non-pathogenic bacteria, and pathogenic smooth (S) bacteria to show that a cell-free bacterial extract of the S strain was capable of converting the R strain to the S strain. What was this principle called?

Solutions

Expert Solution

This principle was called transformation.

Transformation is the mechanism by which gene transfer takes place between bacteria when the donor DNA is cell-free DNA and it is present in the immediate environment of the recipient bacterium.

Oswald Avery, Colin MacLeod, Maclyn McCarty revisited Griffith's experiment. They used rough (R) non-pathogenic bacteria and pathogenic smooth (S) bacteria. When they combined cells of R strain with DNA extract of S strain, transformation takes place.

Then they added DNase to this combination. DNase is the DNA-digesting enzyme. In this case, there was no transformation.

After that, they added RNase to the combination of cells of R strain and DNA extract of S strain. RNase is the RNA-digesting enzyme. In this case, transformation takes place.

Then they added protease to the combination of cells of R strain and DNA extract of S strain. Protease is protein-digesting enzymes. Here transformation takes place.

At last, they added RNase and protease to the same combination of cells of R strain and DNA extract of S strain. Here also transformation takes place.

So, they concluded that the transforming material was pure DNA, not protein or RNA.


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