Molecular Biology Mader-Chapters 13-16
Genetic Material From work on Drosophila, biologists knew that genes were on chromosomes and that genes controlled heredity… What they did not know was the molecular composition of genes Genetic material must: Store information Be replicable Undergo rare change
Griffith’s Transformation Experiment (1931)… What did it prove? There must be a transforming substance that is able to alter the phenotype of an organism This substance was later isolated by Avery, MacLeod, and McCarty in 1944. They exposed the transforming agent to DNAase and Protease to determine that the transforming agent is DNA and not Protein.
Hershey and Chase Transformation Experiment (1952)… What did it prove? This experiment is predicated on the idea that DNA contains P and not S… and Protein contains S and not P DNA of the virus and not the protein of the virus enters the bacteria and conducts the transformation of the bacteria into a viral factory
Structure of DNA Chargaff’s rules: • The amount of A, T, G, and C in DNA varies from species to species but is consistent amongst species • In each species, the amount of A=T and G=C
Watson and Crick Model I guess we should have called it the Watson, Crick, and Franklin Model!
Replication of DNA Replication is Semiconservative • Helicase unzips the DNA • DNA polymerase positions complimentary base pairs • DNA polymerase joins complimentary base pairs Meselson and Stahl’s Experiment… How did it prove that DNA Replication is Semiconservative?
DNA Replication Movies Wiley.com_DNA Replication HHMI 3D DNA Rep. Animation
Prokaryotic vs. Eukaryotic Replication There are distinct differences between prokaryotic and eukaryotic DNA Replication • Prokaryotic DNA Replication • DNA is in a single circular loop • Replication begins in one location • May occur in one direction or in both directions • 10 to the 6thbase pairs are added per minute • Replication complete in 20 minutes • Eukaryotic DNA Replication • DNA is in chromosomes • Begins in numerous locations • Replication fork spreads bidirectional until forks meet • Slower than prokaryotes at 500 to 5000 base pairs per minute • Replication complete in several hours