2 DNA and Chromosomes - Essential CellBiology FourthEdition...

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Chapter 5 DNA and Chromosomes Essential Cell Biology Fourth Edition Copyright  ©  Garland Science 2010
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Figure 5-1a Essential Cell Biology
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Figure 5-1b Essential Cell Biology (© Garland Science 2010)
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Historical Perspective 1666 - Discovery of cells - Hooke 1831 - Discovery of nucleus central feature of cells - Brown 1838 - Cell doctrine - Schleiden & Schwann 1859 - Publication of Origin of Species Darwin 1865 - Laws of segregation & of independent assortment, inheritance was particulate & not blending – Mendel 1902 - Chromosomal theory of inheritance – Sutton & Boveri 1924 - Specific stain for DNA discovered- Feulgen
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Historical Perspective 1925 - Publication of The Theory of the Gene - Morgan 1928 – Bacterial Transformation – Griffith 1941 – One Gene – One Enzyme Hypothesis – Beadle &Tatum 1944 – DNA as physical basis of inheritance- Avery, McCarty & McLeod 1952 – Discovery of A-T & G-C Ratios in DNA – Chargaff Osmotic shock - Hsu Bacteriophage DNA & inheritance – Hershey & Chase 1956 – Accurate determination chromosome number - Tjio & Levan 1953 – Structure of DNA – Watson, Crick & Wilkins 1959 – Chromosome aberrations in man: (Down’s Syndrome - Lejeune; Turner’s Syndrome – Ford) 1970 – Fluorescent & Giemsa Banding Techniques – Caspersson et al.
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Bacterial Transformation - Griffith
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Avery, MacLeod and McCarty Determine DNA is the “Transforming Principle”
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Hershey and Chase Demonstrate That DNA is the Genetic Material
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Three Lines of Evidence that Directed the Double Helix Model 1. Chemical Nature of DNA Components Levene- Nucleotide Building Blocks 2. X-ray Diffraction of DNA Franklin- Uniform Helix, Phosphate Backbone 3. Chargaff’s Rule Purines (G & A) = Pyrimidines (C & T) A = T and C = G
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The Watson Crick Model 1. DNA is (usually) a Right Handed Double Helix- Sugar phosphate backbone on outside, bases on inside 2. The Two Chains Run Antiparallel (opposite polarity) One strand runs 5’ to 3’ and the other runs 3’ to 5’ 3. Bases are Complementary and Held Together by Hydrogen Bonds A base pairs with T (2 H-bonds) C base pairs with G (3 H-bonds) 4. Bases are Planar (flat) and Lying in Pairs Perpendicular to the Axis of the Helix. “spiral staircase” 5. There are 10 base pairs per DNA turn Sequence 6. Sequence on One Strand Dictates the Sequence on the Other Strand
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1. DNA is a Right Handed Double Helix
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2. The Two Strands Run Antiparallel Each strand has structural polarity
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3. Bases are Complementary and Held Together by Hydrogen Bonds
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Spiral staircase 4. Bases are Planar (Flat) and Perpendicular to the Axis of the Helix Note: The sugar phosphate backbones are equidistant apart along the DNA Molecule 2nm width- must be Purine base pairing With Pyrimidine
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5. There are 10 Base Pairs per DNA Turn 3.4 nm Per Turn
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6. Sequence on One Strand Dictates the Sequence on the Other Strand Replication Could Take Place by Unwinding of Helix Each Strand Can Serve as Template for New Synthesis!
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Figure 5-2 Essential Cell Biology (© Garland Science 2010)
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Figure 5-2a Essential Cell Biology (© Garland Science 2010)
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Figure 5-2b Essential Cell Biology (© Garland Science 2010)
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