Bio Final Nov 19 Structure of DNA discovered by Watson and Crich C G T A o James Watson wrote The Double Helix Sketch polynucleotide on final Helix structure with uniform width discovered by Rosalin Franklin Lynus Polling famous chemist first people that said high doses of vitamin C will help cure common cold and DNA is composed of 3 polynucleotides o Franklin proved Lynus wrong because when she looked at the width of the defraction it was too narrow to have 3 polynucleotides Phosphates and sugar are hydrophilic bases are hydrophobic o o 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 wider A double polynucleotide chain forms into a helix DNA is antiparallel one polynucleotide is upside down compared to the other o o Important because hydrogen bonds will only form properly they have to be antiparallel hydroxyl connects with hydroxyl creating a hydrogen bond Structure of DNA suggested a mechanism for its replication Replication 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 rules o o After replication is finished the daughter strand is exactly identical Experiment that supported replication Semi conservative model of DNA replication The parent strands are semi conserved Performed by Messelspin and Stahl Proposed 3 hypothesizes Semi Conservative Model o Models of DNA Replication o o Conservative Model After replication the two daughter strands are have parent and half daughter Parent is completely conserved o o o The parent DNA is some how used to make daughter DNA and some how after the parent DNA is still there Dispersive Model Some how the parent model is used to make daughter but the parent is broken up into random pieces End up with two DNA molecules and they are both pieces of parent and new daughter pieces Density Gradient Centrifugation experiment to figure out hypothesizes Dispersive Model one band of DNA half which is N14 and half N15 Semi Conservative Model lighter band half N14 and half N15 Conservative original band N15 N15 and N14 N14 After round 1 conservative was rejected After round 2 one band N14 N15 and N14 N14 Semi Conservative Wins o Molecular Bases of Semi Conservative Replication Bacteria have one chromosome that s a double helix Replicate chromosome at a place called Ori C origin of Replication 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 middle In Eukaryotes chromosomes are linear Multiple bubbles work together therefore faster Way to learn molecular bases of DNA replication is to learn all about the tool kit prokaryotes and eukaryotes o o Helicase enzyme that unzips the DNA molecule at the replication A series of enzymes flash cards fork by breaking the hydrogen bonds like a triangle the 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 going releases upstream and downstream supercoils nicks o DNA Gyrase
View Full Document
Unlocking...