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Lecture 6

Lecture 6 - Tertiary Structure - BIOL308.pdf

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University of Waterloo
BIOL 308
Bruce Wolff

Lecture 6September25121011 PMBack to tertiary structure of DNABoth Circular and Linear DNAPrimary structure of DNA sugarphosphate chain with purine and pyrimidine bases as side chainsSecondary structure of DNA double helical structure hydrogen bonding between bases stacking interactions phosphate backbone outsideTertiary or higher order structure double stranded DNA both circular AND linear makes complexes with porteins supercoilSupercoilingcoiling of a coilSupercoilsImportant Reduce stress on DNA by twisting the double helixTopological isomers DNA differing only in their states of supercoiling A circular DNA without any superhelical turn is known as relaxed moleculeImportant for packingof DNA circular or linearOne way of making DNA more condensedSupercoiling tells you how packing is possibleDNA helix becomes topographically linearized locally uncoiled during replication and transcriptionDNA functions in replication and transcription depending on its topological stateBase pairing is interruptedDNA molecule exhibits supercoilingStrain is released mainly by writhing into superhelical turnsIt is easier energetically cheaper to bend long DNA then to untwistSupercoiling puts strain on a molecule and DNA must rotate to take the strain offHowever If fixed at both endsSituation in circular DNA molecules AND locally in long linear DNA moleculesIt wants to turn but it cant so it turns anyways and creates supercoil and release stress on bonds and bond anglesOne DNA supercoil superhelical turn forms in the double helix for every 10bp opened for BDNA NOTES FROM LECTURES Page 1
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