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Once opens the molecule, known as "replication bubble" area in it are the "replication forks" is formed. By action of the DNA polymerase nucleotide they enter new fork and connected to the corresponding nucleotide of the source string (A with T, G with C). Prokaryotes open one replication bubble, while multiple eukaryotes. DNA is replicated throughout its length by confluence of the "bubbles".

At Team Meselson and Stahl came up with the following idea:They would take a colony and cultivated in a medium rich in N15, which is a stable isotope nitrogen scanty. Once they will ensure that only DNA containing N15, will take a sample and would separate the DNA by centrifugation.In centrifugation, the components of a mixture are separated according to their weight in the fund are the heavier and lighter compounds above. Since DNA has a different weight to all that is in the cell, it can be separated.And here's the interesting part, because once you identify where in the DNA centrifugation runs, change the means by one without N15 and would observe what results obtained.If the DNA follows the conservative method, then the DNA of the first family would weigh the same because pure N15. The second family had grown up in an environment where there is no N15 and then the DNA would weigh less and be noticed by centrifugation.


To investigate how DNA replication, Meselson and Stahl devised an ingenious way that is based on two fundamental premises, on the one hand is the fact that nitrogen is one of the main elements of DNA, and on the other nitrogenIt has two isotopes that can be distinguished by laboratory techniques.Although 14N is the most abundant isotope of nitrogen, DNA is also feasible with the 15N isotope which is heavier. 15N isotope is not radioactive, it is just heavier than common nitrogen.Thus Meselson and Stahl through intelligent premise of the experiment, they used bacteria and watched replicated their DNA, could obtain information that allowed them to identify the mechanism of DNA replication and eliminating certain alternative theories.

The Meselson-Stahl experiment was conducted in 1957 by Matthew Meselson and Franklin Stahl in which it was shown that DNA replication was semiconservative. A semiconservative replication is one in which the two chain strands of the DNA helix is replicated so that each of the two DNA strands formed from consist of a helix strand of the original and newly synthesized strand.The experiment allowed to confirm the theories of James Watson and Francis Crick about DNA replication method.

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To work DNA polymerase is necessary the presence in the beginning of each new fragment, RNA from small units known as primers, a posteriori, when the polymerase touches the 5 'end of a primer, other enzymes are activated, they remove RNA fragments, DNA nucleotides positioned in place and a DNA ligase joins the chain's growth.

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