Bio Final: Nov 19 Structure of DNA discovered by Watson and Crich C=G, T=Ao James Watson wrote “The Double Helix”Sketch polynucleotide on final******* Helix structure with uniform width discovered by Rosalin FranklinLynus Polling famous chemist, first people that said high doses of vitamin C will help cure common cold and DNA is composed of 3 polynucleotideso Franklin proved Lynus wrong because when she looked at the width of the defraction it was too narrow to have 3 polynucleotides o Phosphates and sugar are hydrophilic, bases are hydrophobico Uniform width of helix- if you try to match the center of the DNA molecule w pyrimidine and pyrimidine it’d be narrow or if you match two purines the molecule would be widerA double polynucleotide chain forms into a helixDNA is antiparallel, one polynucleotide is upside down compared to the othero Important because hydrogen bonds will only form properly they have to be antiparallel (hydroxyl connects with hydroxyl creating a hydrogen bond)o Structure of DNA suggested a mechanism for its replicationReplication: unzip molecule and have an enzyme bring in new nucleotides that are complementary to the parental strand (template to build daughter strand)o Daughter strands made by enzyme using base pairing ruleso After replication is finished, the daughter strand is exactly identicalo Experiment that supported replication: Semi conservative model of DNA replicationThe parent strands are semi conservedPerformed by Messelspin and StahlProposed 3 hypothesizes:-Semi Conservative Modelo Models of DNA Replicationo After replication, the two daughter strands are have parent and half daughtero Parent is completely conserved-Conservative Modelo The parent DNA is some how used to make daughter DNA and some how after the parent DNA is still there-Dispersive Modelo Some how the parent model is used to make daughter but the parent is broken up into random pieces o End up with two DNA molecules and they are both pieces of parent and new daughter piecesDensity Gradient Centrifugation- experiment to figure out hypothesizesDispersive Model= one band of DNA half which is N14 and half N15Semi Conservative Model= lighter band half N14 and half N15Conservative= original band N15/N15 andN14/N14After round 1: conservative was rejectedAfter round 2: one band N14/N15 and N14/ N14Semi Conservative Wins!!o Molecular Bases of Semi Conservative ReplicationBacteria have one chromosome that's a double helix-Replicate chromosome at a place called Ori C (origin ofReplication)-This is where the DNA unzips “soap bubble”-Replication Bubble- in each, there is a replication fork-It unzips DNA molecule by breaking hydrogen bonds that hold it together, forks move different ways away from bubble-3/4ths of way- would have daughter DNA in the middleIn Eukaryotes: chromosomes are linearMultiple bubbles work together therefore fasterWay to learn molecular bases of DNA replication: is to learn all about the“tool kit”- prokaryotes and eukaryoteso A series of enzymes: flash cardso Helicase : enzyme that unzips the DNA molecule at the replicationfork by breaking the hydrogen bonds/ “like a triangle”o DNA Gyrase : releases upstream and downstream supercoils; nicksthe DNA molecule to relieve the supercoils, temporarily break phosphate sugar back bone and lets half spin and leave the other half spin to release the supercoils to allow the helicase to keep
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