12/3/2012

History of DNA-How do we know DNA is the genetic material

I. The Griffith Experiment

 Infecting a mouse with Strep Bacteria (S):
1st. Live S bacteria=dead mouse
2nd. Live R bacteria (no sugar coating like normal S bacteria)=live mouse
3rd. Heat killed S bacteria=live mouse
4th. heat killed S bacteria plus live R bacteria=dead mouse

Conclusion- somehow the genetic information from the "dead" S is being TRANSFERRED into the live R and IT is being TRANSFORMED.

Question- What was the material being transferred?

Transformation: bacteria taking DNA from outside world and taking it into their own genome and reproducing.

II. The Avery Experiments:

Oswald Avery expanded on the Griffith experiment.  He first repeated it to determine that it was valid.  He then isolated the material that was being passed from the killed S to the Live R bacteria and tested that material.  With his testing he determined that this material:
...A. Had the same chemistry as DNA
...B. Had the same behavior as DNA
...C. Was not affected by lipid and protein extraction.
...D. Was not destroyed by protein or RNA digesting enzymes.
...E. WAS DESTROYED by DNA digesting enzymes.

Result:  the material that was being passed was DNA.