Identifying the Substance of Genes (12.1)
Bacterial Transformation Scientists wanted to understand the chemical nature of the gene--they wanted to control the way living things inherit characteristics Griffith He was trying to figure out what made people sick S strain: disease-causing bacteria (smooth edges) R strain: harmless bacteria (rough edges) What caused the mice to get pneumonia?
Griffith’s Experiments Bacterial Experiment with Mice S strain = mice with pneumonia R strain = mice without pneumonia S strain heated = mice without pneumonia because the bacteria were killed with heat S strain heated + R strain = mice with pneumonia (but how?!)
Griffith’s Experiments
Transformation How was it that a mouse contracted bacteria when both the S strain heated and the R strain were both not lethal? Transformation: chemical factor transferred from the heat killed strain (S strain) transferred to the R strain a non lethal strain was transformed into a lethal form the offspring inherited the disease and was able to pass it on = gene
The Cause of Transformation What was the “gene” that allowed for transformation to happen? Avery First experiment: an extracted mixture from the heat killed S strain was treated with enzymes that destroyed proteins, carbohydrates, and RNA transformation occurred = none of those were responsible Second experiment: an extracted mixture from the heat killed S strain was treated with enzymes that destroyed DNA transformation did NOT occur = DNA was responsible DNA stores and transmits genetic information from one generation to the next
Bacterial Viruses Hershey & Chase they studied viruses or how viruses infect living cells Bacteriophages: a kind of virus that infects bacteria it attaches to the bacteria and injects its genetic information into the bacteria (DNA) the viral gene produces new bacteriophages destroying the bacteria cell splits open = hundreds of new viruses
Hershey-Chase Experiment Experiment: Which part of the virus entered the bacteria? Bacteriophage: DNA core and a protein coat Markers (radioactive isotopes) 32P = phosphorus-32 marks DNA 35S = sulfur-35 marks protein Results: the radioactivity in the bacteria contained phosphorus Hershey and Chase confirmed Avery’s results that DNA was the genetic material found in genes in all living things
Hershey-Chase Experiment
DNA DNA makes up genes and is capable of storing, copying, and transmitting the genetic information in a cell. Storing Information Each cell must contain DNA to tell the cell how to develop (eye color, height, oak tree) Copying Information DNA needs to be copied and transmitted to other cells in order to tell the cells what to do. How can this happen if the DNA is in the nucleus? Transmitting Information DNA is transmitted during cell division → Chromosomes have the genes made of DNA → What happens if the information is lost?