Transcript Ch 12
1 Review List the conclusions that Griffith and Avery drew from their experiments Identify Variables What experimental variable did Avery use when he repeated Griffith’s work 2 Review What conclusion did Hershey and Chase draw from their experiments Infer Why did Hershey and Case grow viruses in cultures that contained both radioactive substances? What might have happened if they only used one radioactive substance 3 Choose Griffith, Avery, or Hershey and Chase and develop a flow chart that shows how they used various scientific methods. You may want to refer to Ch 1 for descriptions of the scientific method. CH 12 DNA 12.1 Identifying the Substance of Genes Frederick Griffith Two different strains of same bacteria one strains caused pneumonia Grew both in culture plates. Griffith injected mice with disease-causing bacteria, the mice developed pneumonia and died He injected mice with harmless bacteria, the mice stayed healthy. Griffith took a culture of the S strain, heated the cells to kill them, and then injected the heat-killed bacteria into laboratory Mice survived. He mixed the heat-killed, S-strain bacteria with live, harmless bacteria from the R strain and injected it into laboratory mice Injected mice developed pneumonia, and died. Some chemical factor changed harmless bacteria into disease-causing bacteria was transferred from the heat-killed cells of the S strain into the live cells of the R strain. Transformation Process where one strain of bacteria is changed by a gene from another strain of bacteria. Avery Extracted a mixture of various molecules from the heat-killed bacteria Added enzymes that broke down proteins, lipids, carbohydrates, and RNA Transformation still occurred. Avery’s team repeated the experiment using enzymes that would break down DNA Transformation did not occur DNA is the transforming factor. Hershey and Chase Experiment with bacteriophages Confirmed Avery’s results . Bacteriophages Virus that infects bacteria Attaches to the surface of the bacterial cell Injects its genetic information New bacteriophages are produced. Hershey-Chase Experiment What part of the virus - the protein coat or the DNA core - entered the bacterial cell. Hershey-Chase Experiment Grew viruses in cultures containing radioactive isotopes of phosphorus-32 (P-32) sulfur-35 (S-35) Proteins contain almost no phosphorus and DNA contains no sulfur. If they found S-35 in the bacteria then the virus’s protein coat had been injected into the bacteria If they found P-32 then the DNA core had been injected They mixed the marked viruses with bacterial cells. In the bacteria they found phosphorus P-32 , the marker found in DNA DNA was the genetic material. The Role of DNA Capable of storing, copying, and transmitting genetic information in a cell. Storing Information Main job is of DNA is to store information Genes control patterns of development. Copying Information Before a cell divides, it must make a complete copy of its genes. Transmitting Information When a cell divides each cell receives a complete copy of the genetic information Loss of any DNA during meiosis might mean a loss of valuable genetic information.