tailieunhanh - Lecture Biology - Chapter 14: DNA: The genetic material

After completing this unit, you should be able to: Describe the experiments that first supported the hypothesis that a cell’s hereditary material is located in the nucleus; understand the theory and conclusions associated with the Griffith and Avery experiments using Pneumococcus and mice; explain the evidence that supports the identity of DNA as hereditary material;. | DNA: The Genetic Material Chapter 14 The Genetic Material Frederick Griffith, 1928 studied Streptococcus pneumoniae, a pathogenic bacterium causing pneumonia there are 2 strains of Streptococcus: - S strain is virulent - R strain is nonvirulent Griffith infected mice with these strains hoping to understand the difference between the strains The Genetic Material Griffith’s results: - live S strain cells killed the mice - live R strain cells did not kill the mice - heat-killed S strain cells did not kill the mice - heat-killed S strain + live R strain cells killed the mice The Genetic Material Griffith’s conclusion: - information specifying virulence passed from the dead S strain cells into the live R strain cells - Griffith called the transfer of this information transformation The Genetic Material Avery, MacLeod, & McCarty, 1944 repeated Griffith’s experiment using purified cell extracts and discovered: - removal of all protein from the transforming material did not destroy its ability to transform R strain cells - DNA-digesting enzymes destroyed all transforming ability - the transforming material is DNA The Genetic Material Hershey & Chase, 1952 - investigated bacteriophages: viruses that infect bacteria - the bacteriophage was composed of only DNA and protein - they wanted to determine which of these molecules is the genetic material that is injected into the bacteria The Genetic Material - Bacteriophage DNA was labeled with radioactive phosphorus (32P) - Bacteriophage protein was labeled with radioactive sulfur (35S) - radioactive molecules were tracked - only the bacteriophage DNA (as indicated by the 32P) entered the bacteria and was used to produce more bacteriophage - conclusion: DNA is the genetic material DNA Structure DNA is a nucleic acid. The building blocks of DNA are nucleotides, each composed of: a 5-carbon sugar called deoxyribose a phosphate group (PO4) a nitrogenous base adenine, thymine, cytosine, guanine | DNA: The Genetic Material Chapter 14 The Genetic Material Frederick Griffith, 1928 studied Streptococcus pneumoniae, a pathogenic bacterium causing pneumonia there are 2 strains of Streptococcus: - S strain is virulent - R strain is nonvirulent Griffith infected mice with these strains hoping to understand the difference between the strains The Genetic Material Griffith’s results: - live S strain cells killed the mice - live R strain cells did not kill the mice - heat-killed S strain cells did not kill the mice - heat-killed S strain + live R strain cells killed the mice The Genetic Material Griffith’s conclusion: - information specifying virulence passed from the dead S strain cells into the live R strain cells - Griffith called the transfer of this information transformation The Genetic Material Avery, MacLeod, & McCarty, 1944 repeated Griffith’s experiment using purified cell extracts and discovered: - removal of all protein from the transforming material did not .

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