08-DNA - The Genetic Material • the Hammerling experiment...

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Unformatted text preview: The Genetic Material • the Hammerling experiment • the isolation of nuclein • the Levene tetranucleotide hypothesis • the Griffith experiments • the Avery, MacLeod, and McCarty’s experiment • the Hershey-Chase experiments • the central dogma of molecular genetics • RNA viruses • the elucidation of the structure of DNA • the Watson-Crick model • structure of nucleic acids • the organization of DNA in the eukaryotic nucleus • Method : isolation and purification of nucleic acids • Method : electrophoresis of nucleic acids The Hammerling experiment (1943) • Acetabularia : single-cell green algae Reciprocal graft experiments : • combine the base (containing the nucleus) of A. crenulata with the stem of A. mediterranea (or vice-versa) and observe the regeneration of the cap Results : • in every case the cap regenerated corresponded to that of the species that donated the base • an isolated cap can regenerate a stem but not a base • an isolated stem can regenerate a cap but not a base • isolated base can regenerate the entire cell The cell nucleus contains genetic instructions. A. crenulata A. mediterranea Reciprocal grafts Nucleus in the base determines the type of cap generated. The Hammerling experiment (1943) The first purification of a nucleic acid Friedrich Miescher was a Swiss chemist. • Miescher studied pus samples from the bandages of wounded soldiers at Tübingen University in Germany • he separated the nuclei from the cytoplasm of white blood cells and isolated “ nuclein ” in 1868 • nuclein large amounts of phosphorus, but no sulfur Friedrich Miescher 1844-1895 Phoebus Levene ‘s tetranucleotide hypothesis (1910) Levene proposed a four-nucleotide unit repeated over and over in deoxyribonucleic acid (DNA). 1. Capable of replication . 2. Capable of storing information . 3. Complex enough to generate thousands of proteins (following the expression of genetic information). 4. Any changes in the genetic material ( mutations ) should directly lead to changes in phenotype.* The genetic material must have four properties • Diplococcus strain II R is non-virulent • mice injected with II R survive • no II R cells can be recovered from surviving mice The Griffith experiments (1927) Used mouse bacteria to demonstrate genetic transmission. • Diplococcus strain III S is virulent and kills injected mice • III S cells can be recovered from killed mice The Griffith experiments (1927) Heat kills III S cells, but an unknown transforming agent survives and is capable of transforming II R cells into virulent III S cells. • Transformation : a heritable change in a cell or organism brought about by exogenous DNA • Transforming principle : Griffith’s unknown transforming agent The Avery , MacLeod , and McCarty experiments (1944): identified the transforming principle....
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This note was uploaded on 11/13/2009 for the course PCB 3063 taught by Professor Sotero during the Fall '09 term at University of Central Florida.

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08-DNA - The Genetic Material • the Hammerling experiment...

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