Hershey and Chase confirmed that DNA, and not protein, is the hereditary material.

 In 1952, two researchers, Martha Chase and Alfred
Hershey, set out to test whether DNA or protein was the hereditary material viruses transfer when viruses enter a bacterium.
 Bacteriophage is a virus that infects bacteria.

 Grew bacteriophage (with radioactive sulfur ) in dish of e.coli (sulfur is only found in proteins)
 Grew bacteriophage (with radioactive phosphorous ) in dish of e.coli (phosphorous is only found in DNA)
 They traced the radioactive elements that had entered the e.coli …to see which one was injected into the cell.
 The DNA of the virus and not the proteins was what was in the e.coli causing it to produce more viral DNA.

 Hershey and Chase confirmed that DNA, and not protein, is the hereditary material.

Griffith’s experiments showed that hereditary material can pass from one bacterial cell to another.

 In 1928 Griffith was studying a bacterium called
Streptococcus pneumoniae. He was trying to develop a vaccine against a virulent strain of the bacterium.
 Virulent – ability disease causing
 Vaccine – a substance that is prepared from killed or weakened microorganisms & introduced into the body to protect it from future infection by that microorganism.

 S bacteria is virulent because it has a capsule. The capsule protects it from attacks by the human immune system. It is able to survive long enough in the human body to replicate and cause disease.
 R bacteria is NOT virulent because it lacks a capsule.
Without the capsule it is left defenseless against the human immune system. Therefore it is destroyed in the human body before it is able to cause disease.

 Injected mouse with live R bacteria (w/o capsule).
 NOT Killed mice
 Injected mouse with live S bacteria (w/ capsule).
 kill mice
 Injected mouse with heat killed S bacteria.
 NOT kill mice
 Injected mouse with heat killed S bacteria mixed with live R bacteria.
 Killed mice

 The R bacteria took up the DNA found in the heat killed S bacteria and became virulent!
 The transfer of genetic material from one cell to another cell or from one organism to another organism is called transformation.