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Chapter 13 DNA Structure & Replication Discovery of Structure: Watson, Crick, Franklin, Wilkins 1953 – discovered DNA’s double helix X-ray diffraction Molecule is bombarded by x-rays Way rays scatter gave a hint about DNA structure

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chapter 13

Chapter 13

DNA Structure & Replication

discovery of structure
Discovery of Structure:
  • Watson, Crick, Franklin, Wilkins
  • 1953 – discovered DNA’s double helix
    • X-ray diffraction
      • Molecule is bombarded by x-rays
      • Way rays scatter gave a hint about DNA structure
arrangement of dna
Arrangement of DNA:
  • Structure:
    • Repeating nucleotides:
      • Phosphate group
      • Sugar (deoxyribose)
      • Nitrogenous bases
        • Adenine (A)
        • Guanine (G)
        • Cytosine (C)
        • Thymine (T)
slide7
Spiral staircase:
    • Hand rails: alternating sugar-phosphate
    • Steps: mixture of nitrogen bases
  • Hydrogen bonds link nitrogen bases together
  • Complimentary Base Pairing Rules:
    • Adenine bonds to Thymine (A—T)
    • Guanine bonds to Cytosine (G—C)
  • Purines – 2 rings of carbon and nitrogen
    • Adenine & guanine (Ads Guarantee Purity)
  • Pyrimidines – 1 ring of carbon and nitrogen
    • Cytosine & thymine (Thousands Count Pyramids)
replication
Replication:
  • DNA strand unwinds & hydrogen bonds break
    • Enzyme – helicase
    • Replication fork – where 2 chains separate
  • Complimentary nucleotides are added to free strands from 3 prime ends only
    • Enzyme – DNA polymerase/RNA primase/Okazaki fragments/ligase
  • DNA rewinds and two new identical strands are created
  • Website Demo
    • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html#
proofreading
Proofreading:
  • Mistakes = 1 in every 1 billion
  • DNA polymerases correct any mistakes that occur
mutations
Mutations:
  • Mutation – permanent alteration of a DNA base sequence
    • Point mutations – a mutation of a single base pair
      • Add a T to a G and then correct it to an A-T sequence when it should have been a G-C
mutation examples
Mutation Examples:
  • Cancer:
    • Point mutations that causes uncontrolled cell division
  • Huntington’s Disease
    • A repeat of three bases that cause a mutation
    • Can’t be broken down by nerve cells and builds up causing death
heritable non heritable
Heritable & Non-Heritable:
  • Somatic cells – body cells
    • Non-heritable
    • Skin cancer
  • Germ-line cells – reproductive cells
    • Heritable
    • Huntington’s Disease
causes of mutations
Causes of Mutations:
  • Environment
    • Cigarette smoke; UV light
  • Random
    • Molecular collisions
  • Not all mutations are bad
    • evolution
websites for replication
Websites for Replication:
  • http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter14/animations.html#
  • http://www.johnkyrk.com/DNAreplication.html
  • http://www.phschool.com/science/biology_place/biocoach/dnarep/intro.html
  • http://www.blc.arizona.edu/INTERACTIVE/DNA3/repfork2.gif
  • http://www.contexo.info/DNA_Basics/images/RepFork.gif