Avery Experiments on Transformation

Some substance from the killed S cells has apparently entered the harmless R cells and turned them into deadly S cells.  Griffith called this phenomenon TRANSFORMATION.  
The cells had somehow picked up genes that allowed them to make an S-type carbohydrate capsule. 

HOW DID THE BACTERIA DO THIS TRICK?

Griffith himself was killed in the London Blitz and was never able to discover how his harmless bacteria had been able to acquire new genes that made them deadly.  

In 1944, additional experiments by Avery, McCarty and MacLeod examined the different materials found in an extract of the dead S cells. 
They found that it contained carbohydrates, lipids (fats), protein, DNA and RNA.  

Avery then used enzymes to selectively destroy one of these components.  Then the modified extract was used to try to transform live R cells.  Only one treatment stopped the transformation process:  using enzymes that broke down the DNA in the extract. 

This was the first demonstration that DNA might carried heritable genetic information.  To find out more about DNA, visit the BaseBall on this level.