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Submitted by jiadam on Sun, 04/30/2017 - 21:43

Meselson-Stahl Experiment
This experiment utilized 2 different nitrogens isotopes because nitrogen is a huge component of nucleotides. They were 14N and 15N. 14N is the light nitrogen and is the most abundant on earth. This makes DNA less dense. 15N is the heavy nitrogen which is not as abundant and denser. They used two different nitrogens so that they can be separated by density where the lighter would rise to the top. 15N was placed in E.coli and E.coli replicated the DNA. Using density centrifugation, they were able to see the amount of each nitrogen and which nitrogen it was because of the differences in density. After the first round of replication, the DNA was in the middle of the test tube which can indicate semi-conservative or dispersive because each DNA molecule is half 14N and a half 15N. After the second round of replication, one set of daughter cells were intermediate (half 14N/15N) and the other was lighter which answer the question between semiconservative and dispersive. DNA is replicated semi-conservatively. After numerous rounds, the amount of 14N was significantly more than 15N.

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Great paragraph, this is well written I can tell you took a lot of time thinking about your writing and revising it. I don't have any edits to be made, nice job! 

This is good but I would have not used the same pronoun for two  things on the same sentence like in the "They used two different nitrogens so that they can be separated by density where the lighter would rise to the top" instaed I would say "They used nitrogen isotopes of differing density so that the replicated DNA strands could be seperated based on molecular density". Useing "they" to mean both the scientists and the DNA is a little confusing.