Discovery of DNA and its 3D Structure

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10 Terms

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1869 Fredrich Miescher — his proposal for DNA

  • studied pus cells

  • believed that nuclein (not protein) is the genetic material

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1900s Phoebus Levene — his proposal for DNA

  • renamed nuclein to DNA/RNA

  • discovered nucleotides (sugar, phosphate, and 1 of 4 bases)

  • proposed nucleic acids have a tetranucleotide structure (repeating sequence of 4 nucleotides), TOO SIMPLE

  • tetranucleotide arrangement made the world shift back to protein idea

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1928 Frederick Griffith

  • injects rats with r-strain (rough) & s-strain (smooth = virulent)

  • r-strain - mice lived, s-strain - died, heat killed s-strain - lived, killed s-strain+ living r-strain - died

  • transforming principle — something from the heat-killed bacteria transformed living bacteria (non-pathogenic) to become deadly

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1944 Oswald Avery, Macyln McCarty, Colin MacLeod

  • continued with pneumonia

  • tested for protein, nuclein & DNA

  • destroyed DNA and unable to do transforming principle (proved DNA is used in transformation principle)

  • not ready to publish

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1952 Alfred Hershey, Martha Chase

  • blender experiment — radiolabeled viral proteins (s-35) & viral DNA (p-32) and injected into bacteriophage

  • DNA has no sulfur, proteins has sulfur, no phosphorus (very clever experiment)

  • proved DNA had genetic material

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1949 Erwin Chargaff

  • DNA structure — % composition and base pair rules (A + T, C + G)

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1953 Rosalind Franklin

  • 3D DNA structure —> X-Ray diffraction

  • double helix w/ repeating pattern every 3.4nm & 0.34nm

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1954 Watson & Crick

  • used Chargaff’s rule and Franklin’s findings

  • shows H-bonds, double helix, turn clockwise every 10 nucleotides, 5’ — 3’ direction, antiparallel

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how DNA is wrapped EUKARYOTES

  • wrapped around histones (proteins) for protection & reduce volume

  • nucleosome — group of 8 histones

  • chromatin — nucleosome arranged in loops (scaffold)

  • in mitosis — chromosomes (visible)

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how DNA is wrapped PROKARYOTES

  • DNA resides in nucleoid — no nucleus

  • eubacterial chromosomes are found in loops that join together, making a ring, can supercoil

  • could have plasmids (accessory loops)

  • archaea have circular chromosomes associated with histones