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DNA: Structure and Functions

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  1. DNA: Structure and Functions

  2. Genetic Material • What we know: • Genes are on chromosomes • But what are genes made of? • Genetic material must be: • able to store information • Able to be replicated and transmitted from generation to generation • Able to undergo mutations - variability

  3. Experiments • Miescher – removed nuclei from pus cells, • contained nuclein, rich in phosphorus, not sulfur • Acidic properties: nucleic acids (DNA, RNA)

  4. Griffith experiment – Transformation in Bacteria • 1920’s – vaccine against Streptococcus pneumoniae • S strain – smooth, have capsule • R strain – rough, no capsule • Inject with s-strain, mouse dies • Inject with R-strain, mouse lives • Inject with heat killed S-strain, mouse lives

  5. Bacterial Transformation

  6. When Griffith took a mixture of the heat-inactivated S strain, mixed with the R strain, the bacteria would die.  Thus there was some material in the heat-killed S strain that was responsible for "transforming“ the R strain into a lethal form.

  7. Transformation • Taking up of extraneous genetic material from the environment by bacteria

  8. Avery, MacLeod and McCarty • Produced paper on proving DNA is the transforming material, using enzymes • Enzymes that degrade proteins do not prevent transformation • DNase, enzyme that digests DNA, does prevent transformation • Molecular weight of genetic material would require thousands of nucleotides which equals genetic variability.

  9. Hershey and Chase – DNA or proteins? • Worked with bacteriophages – viruses that infect bacteria • Virus consist of genetic material and a protein capsid • Used radioactive phosphorous to label the core of the phage and radioactive sulfur to label the protein in the capsid of the phage

  10. Results of Hershey and Chase experiment • Viral DNA found in bacteria sediment, viral capsid found in liquid in centrifuged • Concluded that viral DNA, not protein, was responsible for directing the production of new viruses

  11. Alfred Hershey and Martha Chase