DNA Replication

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University of Massachusetts Amherst
Mark Huyler

DNA ReplicationDNA Strands are templates for DNA synthesisWatson and Crick suggested that the existing strands of DNA served as a template for the producing of new strands with bases being added to the new strands according to complementary base pairingBiologists then proposed three alternative hypotheses for how the old and new DNA strands interacted during replicationSemiconservative replicationConservative replicationDispersive replication In semiconservative replication the parental DNA strands separate and each is used as a template for the synthesis of a new strandDaughter molecules each consist of one old and one new strandIn conservative replication the parental molecule serves as a template for the synthesis of an entirely new moleculeIn dispersive replication the parental molecule is cut into sections such that the daughter molecules contain old DNA interspersed with newly synthesized DNA Meselson and Stahl showed that each parental DNA strand is copied in its entirety but did not illustrate a mechanism for this processThe discovery of DNA polymerase the enzyme that catalyzes DNA synthesis cleared the way for understanding DNA replication reactionsArthur Kornberg et al were credited with isolating the first DNA polymerase and in 1959 won the Nobel prize PhysiologyMedicineA critical characteristic of DNA polymerases is that they can only work in one directionDNA polymerases can add deoxyribonucleotides to only the 3 end of a growing DNA chain As a result DNA synthesis always proceeds in the 53 directionDNA polymerization is exergonic because the monomers that act as substrates in the reaction are deoxyribonucleoside triphosphates dNTPs which have high potential energy because of their three closely packed phosphate groupsAssume that the following single strand of DNA was synthesized using DNA polymerase and standard ATP GTP and CTP along with a form of TTP that had each of the three 32phosphates labeled with P 5GGTTGAACATGG3To determine how nucleotides are linked together an investigator cleaved the newly formed strand with the enzyme spleen diesterase which cleaves DNA at the covalent bond connecting the 5 carbon of the sugar to the phosphate Which of the resulting nucleotides would you expect to now 32carry the Pa A only b T onlyc T A G d C T G AHow does replication get startedA replication bubble forms in a chromosome that is actively being replicated
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