2.1 HSW - Unravelling the Role of DNA

• what molecule did scientists think carried genetic information?


  proteins because of their chemical diversity

  DNA was considered to be too chemically simple to carry out the role
• how do scientists for hypothesis?


  by using observations and current knowledge
• how do scientists accept/reject a hypothesis?


  make predictions of a particular investigation then carrying it out many times and collecting lots of experimental evidence
• bwhat was used to test hypothesis of DNA


  mice & bacterium that can cause pneumonia
• what a forms does the bacterium exist in?

  R-strain: safe, doesn't cause pneumonia

  S- strain: causes pneumonia, harmful
• Method used to test hypothesis using mice & bacterium


  Mice were separately injected with living form of safe bacteria & dead forum of harmful bacteria - both groups remained healthy

  when injected with both bacterium both groups got pneumonia & living form of harmful bacteria were extracted from the groups
• what was the second part of the experiment involving mice & bacteria?

  various substances from living harmful bacteria from Mice were isolated and purified

  only substance that produced harmful bacteria was DNA and when enzyme that broke down DNA was added this stopped
• testing hypothesis of DNA Using viruses


  protein & DNA in viruses were labelled with a different radioactive element

  one sample of bacteria was infected by viruses with radioactive protein, the other with vines with radioactive DNA

  only sample Of bacteria infected by virus with radioactive DNA showed signs of radioactivity