biol Chapters 9-13

biol Chapters 9-13 - DNA: The Molecule of Heredity Chapter...

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DNA: The Molecule of Heredity Chapter 9 How did scientists discover genes are made of DNA? Griffith Discovers Transformation (Figure 9-1) Avery, MacLeod, and McCarthy What is the transforming material? o Cell extracts treated with protein, carbohydrate, and RNA digesting enzymes could still transform bacteria o Cell extracts treated with DNA-digesting enzymes lost their transforming ability o Conclusion: DNA transforms bacteria DNA Structure Nucleotide Bases in DNA (page 151) Each nucleotide has a phosphate, deoxyribose sugar, and N-containing base Three types of nucleotides in DNA (thymine, cytosine, adenine, guanine) determined by structure of N-containing base A Nucleotide Strand Always assembled from P end to S end Covalent bond between the sugar of one nucleotide and the phosphate of a second The Watson-Crick Model of DNA Structure (figure 9-3) DNA is a double helix of 2 nucleotide strands Complementary base pairs hold the 2 nucleotide strands together Complementary strands run in opposite directions Base Pairing in DNA Chargaff’s rule A=T (adenine bond s with thymine) -forms 2 hydrogen bonds C=G (cytosine bonds with guanine) -forms 3 hydrogen bonds X-ray Diffraction of DNA Maurice Wilkins and Rosalind Franklin knew that DNA formed some sort of helix by the patterns seen in x-ray diffraction The Discovery of DNA Pauling (USA) Wilkins and Franklin (England) Watson and Crick (USA) first described structure of DNA Genetic Code (DNA can encode a lot of information)
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Along a single DNA strand, the order of nucleotides determines order of amino acids in proteins Computers: 0 and 1 codes for everything DNA: A, T, C, and G codes for everything DNA strand 10 nucleotides long has 4 10 different possible combinations (1,048,576) Some human chromosomes are 250,000,000 nucleotides long (4 250,000,000 =GOOO!) How does DNA replication ensure genetic consistency? DNA structure helps explain how it duplicates DNA is two nucleotide strands held together by hydrogen bonds Hydrogen bonds between two strands are easily broken Each single strand then serves as a template for a new strand DNA Replication (figure 9-4) Separation of parental DNA helix Incorporation of complementary nucleotides Two daughter helices (one old strand and one new strand) Semi conservative Replication Model One DNA double helix splits, duplicates strands to make sister chromatids on the duplicate chromosome. Enzymes in Replication DNA helicase -unwinds the two strands and breaks the hydrogen bonds DNA polymerase -attaches complementary nucleotides DNA ligase -fills in gaps (makes covalent bonds) Replication Mechanism (figure E9-2) Continuous and Discontinuous Assembly Strands can only be assembled in the P to S direction DNA ligase fills in gaps on discontinuous strand Gene Expression and Regulation Chapter 10 How do we go from genes to physical structure?
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This note was uploaded on 04/28/2008 for the course BIOL 1001 taught by Professor Minor during the Fall '08 term at LSU.

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biol Chapters 9-13 - DNA: The Molecule of Heredity Chapter...

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