DNA Structure

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Chapter 13

• DNA Structure Replication

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Discovery of Structure

• Watson, Crick, Franklin, Wilkins
• 1953 discovered DNAs double helix
• X-ray diffraction
• Molecule is bombarded by x-rays
• Way rays scatter gave a hint about DNA structure

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James Watson (left) Francis Crick (right) with
DNA model shortly after publication
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Rosalind Franklin her X-ray diffraction image
of DNA
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Arrangement of DNA

• Structure
• Repeating nucleotides
• Phosphate group
• Sugar (deoxyribose)
• Nitrogenous bases
• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T)

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Components of DNA
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• 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 (AT)
• Guanine bonds to Cytosine (GC)
• Purines 2 rings of carbon and nitrogen
• Adenine guanine (Ads Guarantee Purity)
• Pyrimidines 1 ring of carbon and nitrogen
• Cytosine thymine (Thousands Count Pyramids)

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Complementary Base Pairs
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Extraction of DNA from Strawberries
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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/s
  tudent_view0/chapter14/animations.html

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Proofreading

• Mistakes 1 in every 1 billion
• DNA polymerases correct any mistakes that occur

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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

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Mutation Examples

• Cancer
• Point mutations that causes uncontrolled cell
  division
• Huntingtons Disease
• A repeat of three bases that cause a mutation
• Cant be broken down by nerve cells and builds up
  causing death

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Heritable Non-Heritable

• Somatic cells body cells
• Non-heritable
• Skin cancer
• Germ-line cells reproductive cells
• Heritable
• Huntingtons Disease

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Causes of Mutations

• Environment
• Cigarette smoke UV light
• Random
• Molecular collisions
• Not all mutations are bad
• evolution

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Websites for Replication

• http//highered.mcgraw-hill.com/sites/0072437316/s
  tudent_view0/chapter14/animations.html
• http//www.johnkyrk.com/DNAreplication.html
• http//www.phschool.com/science/biology_place/bioc
  oach/dnarep/intro.html
• http//www.blc.arizona.edu/INTERACTIVE/DNA3/repfor
  k2.gif
• http//www.contexo.info/DNA_Basics/images/RepFork.
  gif