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Chapter 13

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

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  1. Chapter 13 DNA Structure & Replication

  2. 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

  3. James Watson (left) & Francis Crick (right) with DNA model shortly after publication

  4. Rosalind Franklin & her X-ray diffraction image of DNA

  5. Arrangement of DNA: • Structure: • Repeating nucleotides: • Phosphate group • Sugar (deoxyribose) • Nitrogenous bases • Adenine (A) • Guanine (G) • Cytosine (C) • Thymine (T)

  6. Components of DNA

  7. 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)

  8. Complementary Base Pairs:

  9. Extraction of DNA from Strawberries

  10. 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#

  11. Proofreading: • Mistakes = 1 in every 1 billion • DNA polymerases correct any mistakes that occur

  12. 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

  13. 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

  14. Heritable & Non-Heritable: • Somatic cells – body cells • Non-heritable • Skin cancer • Germ-line cells – reproductive cells • Heritable • Huntington’s Disease

  15. Causes of Mutations: • Environment • Cigarette smoke; UV light • Random • Molecular collisions • Not all mutations are bad • evolution

  16. 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

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