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Lecture 11

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Western University
Biology 1202B
Brenda Murphy

1DNA Structure and Organization Chapter 12 Human Genome 1952HersheyChase o Studied E Colio The genetic material of the phage viruses that infect bacteria was DNA not proteinThe isotope used to label proteins was found in phage coats after infection but was not found in the infected cell or in progeny phages Therefore protein is not the genetic material o Established the term Transformationthe conversion of a cells hereditary type by the uptake of DNA released by the breakdown of another cell 1953Watson CrickFranklin o Used an Xray diffraction model to study the structure of DNA Xray beam is directed at a molecule in the form of a crystal and the rays are reflected into smaller beams that exit the crystal and definite angles determined by the arrangement of atoms in the structure of the crystal The DNA molecules within the fibre were cylindricalabout 2nm in diameterMajor patterns of atoms repeated at intervals of 034 nm and 34 nm within the DNA Distance between each pair of bases034 nmEach full twist of the DNA double helix34 nm o DNA structure is a double helix Two polynucleotide chains twist around each other in a righthanded way like a doublespiral staircaseo DoubleHelix ModelTwo sugar phosphate backbones are separated from each other by a regular distanceComplimentary Base PairingThe bases extend into and fill this central space purinepyrimidine base pairs in DNA are AT and GCStabilized by hydrogen bonds2 between AT and 3 between GCTwo strands of a double helix fit together in a stable chemical way if they are antiparallelRun in opposite directions 3 of one strand is opposite to the 5end of its complimentary strand o DNA Replication Model SemiConservative Replication Two chains unwind and separateEach old strand is a template for the addition of complimentary basesEach of the two new double helices consists of identical basepairing sequences as the parental DNA
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