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Miescher
Miescher was reasearching the compostion of white blood cells which he found in great quantities in the pus from infections; later on he used salmon sperm as a source. He then isolated the "nuclein," DNA, from cell nuclei and was the first to identify DNA as a distinct molecule -
Chargaff
Chargaff examined DNA in an organism and found that the ratios of the components in the DNA was consistent within an individual organism; meaning that base pairs in DNA,A to T and C to G, are in equal proportions to each other. However, when he looked at the ratios of DNA bases across different species,they differed Chargaff then concluded that the proportions of bases depended on the species the DNA had come from. This information was later on used to discover the double-helix structure of DNA. -
Hershey and Chase
Hershey and Chase proved that DNA was the genetic material,not protein, through the blender experiment.They showed that the DNA of the phage virus contains the phage genes.After a phage particle attaches to a bacterium,its DNA enters through a tiny hole while its protein coat remains outside.The key to the success of the experiment was showing that viral infection was unaffected by violent agitation in a kitchen blender,which removed the empty viral protein shells from the bacterial surface. -
Watson and Crick
Watson and Crick used Franklin's x-ray diffraction photos of the "wet" form of DNA to suggest the molecule was made of two chains of nucleotides in a helix,but one going up and the other going down changing everything that was currently know at that time period.During cell division the two strands separate and on each strand a new complementary half is built and that the matching base pairs interlocked in the middle of the double helix.This way DNA can reproduce without changing its structure. -
Franklin
Franklin used a x-ray diffraction of the "wet" form, in higher humidity,of a DNA molecule to show clearly that DNA was a double helix. A finding that contradicted the widespread theory that the structure had three chains.With Franklin's discovery, which Watson and Crick took credit for, all of what society knows about DNA would be false. -
Meselson and Stahl
Meselson and Stahl proved how DNA replicated by culturing bacteria in a 15N medium,then shifting the bacteria to a 14N medium.After one replication cycle,the DNA was all of intermediate density ruling out the conservative replication model.After two replication cycles,two bands of DNA were seen,one of intermediate density and one of light density proving the semi conservative model true.Their discovery added a new understanding of how DNA replicates itself.
