Evidence for the semi conservative replication of DNA Flashcards
who carried our the experiments to prove the semi conservative replication of DNA
Messelson and Stahl, 1950s
what isotopes of nitrogen were used
14N and the heavier 15N
Three theoretical methods of DNA replication
conservative, semi conservative, dispersive
describe the dispersive method
Segments of the double strand remain in the daughter helicies and the rest is made of new nucleotides
describe the conservative method of replication
the whole double strand structure is replicated to produce a daughter helix, no new nucleotides are added
in which generation is conservative replication disproved
Generation 1 because conservative would only have produced the heavy weight band again, without the new intermediate band aswell
in which generation is dispersive replication disproved
generation 2 bc dispersive would have only produced an intermediate band, not the lightweight too
Describe the process of generation 0
bacteria grown in a medium containing only 15N isotope
what in DNA contains nitrogen
the nitrogenous bases
result of spinning the DNA from gen 0 in a centrifuge
single band low in test tube (heavy)
describe Messelson and Stahl’s experiment
Grow bacteria in a medium of only the 15N isotope (gen 0)
Purify the DNA and spin in a centrifuge to determine density of DNA
Repeat for 2 generations, allowing same bacteria to instead grow in a medium containing 14N isotope and compare densities of DNA produced
Name of method used to test density of DNA produced
separation by centrifugation
result of spinning gen 1 DNA
Single band in the middle of the test tube (intermediate DNA)
Result of spinning gen 2
two bands: one in the middle and ont at the top, (intermediate and light DNA respectively)
what did centrifuge tube contain
cesium chloride, very dense, similar density to DNA
