DNA Deoxyribose nucleic acid Composed of nucleotides store
DNA - Deoxyribose nucleic acid • Composed of nucleotides • store and transmit genetic information • replicate • undergo changes (mutate) 1
DNA (Deoxyribonucleic Acid) A. Found in almost all living cells –in the nucleus of eukaryotes (3 Feet/Cell) B. 2 primary functions 1. Control protein (enzyme) production-These enzymes then control chemical reactions in cells. 2. Duplicate itself for new cells that are created 2
Nucleotide • Deoxyribose sugar • Phosphate group • Nitrogenous base – A, T, C, G 3
Nitrogenous Bases • 4 Bases – Adenine (A), Thymine (T), Cytosine (C), Guanine (G) • Purine – Double ring – A and G • Pyrimidine – single ring – T and C 4
Frederick Griffith: Transformation 1928 • Discovered that bacteria could give other bacteria heritable traits, even after they were dead. 5
Avery, Mc. Carty & Mac. Leod: Griffiths Refined (1944) • Refined Griffith's Experiment • Exposed R-strain Streptococcus to purified Sstrain protein, and purified S-strain DNA • Only the bacteria exposed to the S-strain DNA were transformed 6
Hershey & Chase: The "Blender" Experiment (1952) • Worked with bacteriophages • Conclusively demonstrated that DNA was the molecule of heredity • Tagged phage DNA and protein with radioactive atoms and tracked the transmission of that radioactivity to infected bacteria • Nobel Prize: Hershey (1969) 7
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Chargaff’s Rule • Amount of guanine equals amount of cytosine – Amount of adenine equals thyamine • Chargaff’s rule: C=G A=T 9
Watson & Crick, Franklin & Wilkins (1953) 10
• Two competing teams to determine the structure of DNA • Watson and Crick used X-ray diffraction data developed by Rosalind Franklin to develop their "double helix" model of DNA • Nobel Prize: Watson, Crick & Wilkins (1962) 11
DNA is a Double Helix James Watson and Francis Crick **Similar to ladder that is twisted** • Sugar and phosphate form the backbone • Bases lie between the backbone – Nucleotides • A, G, T, C – Held together by H-bonds between the bases • A-T – 2 H bonds • G-C – 3 H bonds 12
Orientation of DNA • The nucleotides form a chain • Phosphate end is the 5' end – The opposite end (sugar) is the 3' end • Q: Since DNA is complementary, what end matches with the 5’ end? 13
• Bases on one strand are covalently bonded to each other ("phosphodiester bonds") • Bases on opposite strands are hydrogen bonded to each other ("base pairs"). • Adenine = Thymine (2 H bonds) • Cytosine = Guanine (3 H bonds) 14
Forms of DNA 1. Chromatin –Partially unwound (Normal Situations) 2. Chromosome – tightly wound DNA (Cell division) 15
Chromosome Structure • DNA wraps around histones • histones form nucleosome Chromatin Fibers Histones Nucleosomes 16
Plasmids • small, circular, double-stranded DNA molecule – Different from chromosomal DNA • naturally exist in bacterial cells • Often provide bacteria with genetic advantages – antibiotic resistance • Hundreds to thousands of base pairs • each daughter cell receives a copy of plasmid • Bacteria can also transfer plasmids to one another through conjugation 17
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