EXAM 2 Experiments

Hershey andChase did an experiment where they infected E.coliwith a virus (bacteriophage) in order to determine the molecule of inheritance(genetic material).

They designed an experiment to see what virus cells passed to the host when they infected them.

They found that DNA was passed inside the cell and passed on to progeny

They determined that the 3D shape of DNA is a double helix.

She x-rayed DNA fragments that were Watson and Crick used to interpret it as a double helix.

• They tested 3 models for DNA:
• 1. conservative: parental strand remains the same and the new strand has completely new DNA
• 2. Semi-conservative: Each helix has onw new strand and one old strand
• 3. Disperse: Each strand is a mixture of new and old DNA.

Semi-conservative theory was proved correct after several generations of testing

• His experiment  was the transformation of Streptococcus.
• He determined that dead S bacteria contained a substance that transformed R bacteria into pathogenic S strain!

They determined that DNA is the transforming factor (and  not RNA or protein).