Lecture 14 - DNA

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15 Terms

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structure of chromosomes

  • DNA - 4 nucleotide

  • protein - 20 amino acids


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Frederick Griffith

  • worked in the pneumonia vaccine

  • 1st to show evidence again protein hypothesis

  • his experiment:

    • rough strand of pneumonia are nonpathogenic (did not cause pneumonia) and smooth strand causes pneumonia

    • gave each type of strand to mice (smooth, rough, heat killed smooth, and combination of rough & heat-killed)

    • in the combination smooth became active

    • demonstrated transformation

    • bacteria can transfer genetic information → DNA could be passed between cells


<ul><li><p>worked in the pneumonia vaccine</p></li><li><p>1st to show evidence again protein hypothesis</p></li><li><p>his experiment:</p><ul><li><p>rough strand of pneumonia are nonpathogenic (did not cause pneumonia) and smooth strand causes pneumonia </p></li><li><p>gave each type of strand to mice (smooth, rough, heat killed smooth, and combination of rough &amp; heat-killed)</p></li><li><p>in the combination smooth became active</p></li><li><p>demonstrated transformation</p></li><li><p>bacteria can transfer genetic information → DNA could be passed between cells</p></li></ul></li></ul><p></p>
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transformation

change in genotype or phenotype due to assimilation of external DNA

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Avery, MacLeod, McCarty

experiment:

  • lysed(broke open) S(smooth) cells

  • isolated each component (lipids, carbs, protein, & DNA)

  • tested each component to see which one transformed rough to deadly smooth cell

  • only nucleic acid/DNA successfully transformed suggesting DNA carries genetic information


<p>experiment:</p><ul><li><p>lysed(broke open) S(smooth) cells</p></li><li><p>isolated each component (lipids, carbs, protein, &amp; DNA)</p></li><li><p>tested each component to see which one transformed rough to deadly smooth cell</p></li><li><p>only nucleic acid/DNA successfully transformed suggesting DNA carries genetic information</p></li></ul><p></p>
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Hershey & Chase

experiment:

  • used bacteriophage T2

    • virus that infects bacteria

    • 2 components - DNA/RNA and protein

  • radiolabeled the components and infected bacteria

    • protein was chemically labeled with sulfur

    • DNA was chemicallly labelled with phosphorus

  • after blending & centrifugation, was of the radiative phosphorus was still found inside → DNA is the molecule of heredity


<p>experiment:</p><ul><li><p>used bacteriophage T2</p><ul><li><p>virus that infects bacteria</p></li><li><p>2 components - DNA/RNA and protein</p></li></ul></li><li><p>radiolabeled the components and infected bacteria</p><ul><li><p>protein was chemically labeled with sulfur</p></li><li><p>DNA was chemicallly labelled with phosphorus</p></li></ul></li><li><p>after blending &amp; centrifugation, was of the radiative phosphorus was still found inside → DNA is the molecule of heredity</p></li></ul><p></p>
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DNA structure

  • made of nucleotides - monomer of nucleic acids

  • double helix

  • 3 parts: sugar, nitrogenous base, phosphate


<ul><li><p>made of nucleotides - monomer of nucleic acids</p></li><li><p>double helix</p></li><li><p>3 parts: sugar, nitrogenous base, phosphate</p></li></ul><p></p>
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nitrogenous bases

  • purine

    • adenine & guanine

  • pyrimidine

    • cytosine & thymine


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Erwin Chargaff

  • studied chemical composition of DNA

  • his rules:

    • total purine (A+G) = total pyrimidine (C+T)

    • A = T, C=G

    • A+T does not equal C+G


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Rosalind Franklin

  • x-ray crystallographer

  • determined:

    • DNA is a double helix

    • bases are inside

    • diameter

    • distance between turns

    • nucleotides per turn


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<p>Watson &amp; Crick</p>

Watson & Crick

  • used information from Chargaff and Frankline

  • published the DNA model

    1. double helix - 2 strands of DNA would around each other

      • 1 “DNA molecule” = 1 double helix

    2. each strand has 2 regions - sugar/phosphate backbone & nitrogenous bases

      • alternating constant sugar & phosphate that are outside the helix

      • nitrogenous bases are inside the helix that contains the information

    3. strands held together with H-bonds

      • A-T based pairs form 2 H-bonds

      • G-C based pairs form 3 H-bonds

    4. strands are antiparallel

      • carbons in sugar numbered 1’-5’

      • 5’ always has phosphate

      • 3’ always has hydroxyl

    5. base pairings

      • always purine with pyrimidine

      • A w/ T, C w/ G

      • strands are complementary


<ul><li><p>used information from Chargaff and Frankline</p></li><li><p>published the DNA model</p><ol><li><p>double helix - 2 strands of DNA would around each other</p><ul><li><p>1 “DNA molecule” = 1 double helix</p></li></ul></li><li><p>each strand has 2 regions - sugar/phosphate backbone &amp; nitrogenous bases</p><ul><li><p>alternating constant sugar &amp; phosphate that are outside the helix </p></li><li><p>nitrogenous bases are inside the helix that contains the information</p></li></ul></li><li><p>strands held together with H-bonds</p><ul><li><p>A-T based pairs form 2 H-bonds</p></li><li><p>G-C based pairs form 3 H-bonds</p></li></ul></li><li><p>strands are antiparallel</p><ul><li><p>carbons in sugar numbered 1’-5’</p></li><li><p>5’ always has phosphate</p></li><li><p>3’ always has hydroxyl</p></li></ul></li><li><p>base pairings</p><ul><li><p>always purine with pyrimidine</p></li><li><p>A w/ T, C w/ G</p></li><li><p>strands are complementary</p></li></ul></li></ol></li></ul><p></p>
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primase

brings in RNA primer; can start a new strand without a free 3’ hydroxyl

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helicase

unwinds the double helix in DNA replication

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origin of replication

a specific genetic sequence where DNA replication begins

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semi-conservative replication

  • each existing strand acts as the template for a new strand

  • proposed by Watson & Crick, confirmed by Meselson and Stahl


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DNA replication

  • semi-conservative

  • 2 parts:

    • intiation

    • elongation