Matthew Meselson and Franklin Stahl are famous for their DNA replication experiment. Meselson and Stahl conducted the experiment that supported the hypothesis formulated by Watson and Crick that DNA replicates. The aim of the experiment was to provide an explanation of the structure of James Watson and Francis Crick's DNA. The model represented DNA as two helical strands joined into a double helix that replicated in a semi-conservative manner. The experiment took place in the 1950s, following a debate among scientists about how DNA replicated. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay In 1956, Meselson and Stahl began their experiment. Matthew and Franklin completed many projects together, including DNA replication. Most of their projects used a method created by Meselson in 1954: density gradient centrifugation. Density gradient centrifugation separates molecules based on their density based on the molecular weight of the molecules. This technique was used in the DNA replication experiment to separate DNA molecules in a solution. In October 1957, Meselson and Stahl began the experiment with E. coli containing only the heavy isotope of nitrogen (15N) to make the parental DNA higher than normal density. As the bacteria grew, they duplicated themselves, thus replicating their DNA. They then added an excess of light nitrogen isotopes (14N) to the heavy nitrogen environment. Meselson and Stahl grew E. coli in the 14N isotopic environment for all subsequent generations, so that any new DNA strands produced were of lower density than the original parent DNA. Before adding 14N nitrogen, the scientists extracted samples of E. coli growth medium for testing; They centrifuged each sample for initial separation, then added salt to the bacteria so that they released their DNA contents, allowing them to analyze the samples. Then, they performed a density gradient centrifugation for each DNA sample to see the parental pathway. and daughter DNA distributed according to their densities. They added a small amount of each sample to a solution of cesium chloride. The researchers spun the DNA in an ultracentrifuge for twenty hours until the DNA reached equilibrium. Using ultraviolet light, the scientists photographed the resulting DNA bands, which showed peaks in DNA concentrations at different densities. The density of DNA depends on the amount of nitrogen present. Which means that the more 15N atoms present, the denser the DNA. For previously collected bacterial DNA, UV photographs showed only a single band for DNA containing the 15N isotopes. This happened because the DNA from the first sample grew in an environment containing only 15N isotopes. For samples taken during the first replication cycle, photographs showed weaker 15N DNA bands. Additionally, a new DNA band was formed representing half of the 15N DNA isotopes and half of the 14N DNA isotopes. Toward the end of the first replication cycle, the heavy DNA band disappeared. All that was left was a band of half 15N and half dark 14N dark DNA. Data from the first replication cycle showed some distribution of parental DNA, as only parental DNA contained 15N nitrogen isotopes and only parental DNA could account for 15N nitrogen isotopes in daughter DNA . Trends.