Unit 3 Nucleic Acids

Nucleic Acid-  A large complex organic molecule that stores and transmits genetic information  DNA & RNA

Evidence  Supporting the role of DNA in living things

Transformation-  To change from one form to another

Transformation Experiment  S. Pneumoniae Bacteria  R strain- harmless  S strain- virulent (disease causing)  Mice

Experiment 1 with Bacteria (p194)  R cells  injected  mice live

Experiment 2 with Bacteria (p194)  S cells  injected  mice die

Experiment 3 with Bacteria (p194)  Heat killed S cells  injected  mice live

Experiment 4 with Bacteria (p194)  R cells + heat killed S cells  injected 

Question  1. Based on results of Exp 1, 2, & 3, what do you think happened in Exp 4?  Answer- Mice Live  2. Could cells injected in Exp 4 cause pneumonia before they were injected?  Answer- No

Experiment 4 with Bacteria (p194)  R cells + heat killed S cells  injected  mice die

Questions  3. How did the bacteria that resulted in Exp 4 differ from ones injected?  Answer- Living S cell present.  Read through the Extension  4. Was this difference only in their structure?  Answer- No, since trait is passed on, the genetic message must also have been changed.

Questions  5. Give an explanation as to what happened in Exp 4.  Answer- DNA from heat killed S cells used in R cells & changes them into living virulent S cells

Transforming Factor-  Factor that causes the transformation-  Avery tested in 1940’s, determined it was DNA

Bacteriophage (p. 195)  A virus that infects a bacteria  Consists of a protein coat and DNA  Problem- Is it the protein coat or DNA that is hereditary material a virus transfers to a bacterium?

Hershey-Chase Experiment (p 195 )  1. Used radioactive sulfur to tag protein coat.  2. Used radioactive phosphorous to tag the DNA.  3. Used blender to separate the virus coat from bacteria.  Detected radioactive phosphorous in the bacteria. Concluded DNA enters bacteria.

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