Lec 8 DNA & replication

Lec 8 DNA& - complementary A adj 1 a Forming a complement completing perfecting b Of two(or more things Mutually complementing or

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complementary A. adj. 1. a. Forming a complement, completing, perfecting. b. Of two (or more) things: Mutually complementing or completing each other’s deficiencies. Source: Oxford English Dictionary Online, http://dictionary.oed.com
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&The double helical model suggested a semiconservative model for DNA replication. for synthesis of new strands. will be complementary to the template. the sequence of bases. sequence. Complementary-strands provide a means for correcting damage or copying errors sufficiently strong for a stable helix, yet can be pulled apart to allow replication and transcription. ±It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.² Watson & Crick, Nature vol 171, pp 737-8, April 25, 1953
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Watson and Crick reasoned that the hydrophilic phosphates would lie on the outer surface with the more hydrophobic bases in the center. hydrophobic hydrophilic
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Chargaff found a striking relationship in the molar ratios of two pairs of bases: A = T and G = C. In contrast, the A+T and G+C contents varied among organisms. N N N N C C C C C C C C C N N adenine thymine O H H O deoxyribose H N H H H N N N N C C C C C C C C C N N cytosine guanine N H O H O H H N H H H H CH 3 moles of adenine = moles of thymine moles of guanine = moles of cytosine By modeling Watson and Crick found that hydrogen bonding between A and T and between G and C, δ δ δ δ δ + δ + δ + δ + Note that both base pairs have the same overall geometry. δ + δ deoxyribose deoxyribose deoxyribose
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Franklin and Wilkins collected x-ray diffraction data on DNA fibers that indicated an anti-parallel, right-handed, double helix with a helical periodicity of 3.4 nanometers and 10 repeating units per helical turn. By modeling, Watson and Crick found that their base pairing scheme could be accommodated by anti- parallel sugar phosphate strands. In addition to the hydrogen bonding, the two strands are stabilized by stacking of the hydrophobic bases. View along helical axis showing base stacking The striking feature of the model: the two antiparallel DNA strands have complementary base sequences dictated by A-T and G-C hydrogen bonding. 5&
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major groove minor groove 10 bp 0.34 nm/bp hydrogen-bonding base surfaces double helix antiparallel strands phosphate 2-deoxyribose
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Building blocks are nucleotides made up of phosphate, deoxyribose and purine or pyrimidine bases. DNA strands are chains of nucleotides connected by phosphodiester
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This note was uploaded on 07/17/2011 for the course BIO 151 taught by Professor Grinblat during the Summer '08 term at Wisconsin.

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Lec 8 DNA& - complementary A adj 1 a Forming a complement completing perfecting b Of two(or more things Mutually complementing or

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