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1.https://www.youtube.com/watch?v=MbxkiEmi5TU
2.https://www.mun.ca/biology/scarr/iGen3_03-01.html
3.https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=2ahUKEwiL99mSiI3kAhUIKFAKHRXGBZUQjB16BAgBEAM&url=http%3A%2F%2Fwww.biologie-schule.de%2Fmeselson-stahl-experiment.php&psig=AOvVaw0ZvHn-Api8rfCqvyWPiuEd&ust=1566239818829550

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Proof of Semi-conservative model and disprove of conservative as well as dispersive replication model

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Proof of Semi-conservative model and disprove of conservative as well as dispersive replication model

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Through the outcome of this process we can see a gradient in solution density  in relation to generations produced. The first generation consists solely of n15 E. coli. This can be linked to all three theories, however after the first replication process we see a mixture of n15 E. coli as well as n14 E. coli, which means it cannot be the conservative model at this point, because if this was the case we would have a 100% light nitrogen level as well as a 100% heavy nitrogen copy. This is due to the theory suggesting an identical replica of helix, as mentioned. The dispersive model is disproved after the first appearance of a only-light nitrogen consisting E. coli level, as fragments of n15 would have always been found in the daughter molecules. This would have only shown heavy nitrogen settlement and mixture levels above this n15 settlement.

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The theory of conservative replication suggests, that the parental DNA molecule synthesizes an identical copy, producing the conserved two strands in helix form, as well as the newly formed copy also existing in this manner. In the second replication cycle this process is repeated, as seen in the model given.

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The theory of Semi conservative replication suggests, that the parental DNA molecule unzips into two individual strands which each produce a copy of themselves. This results in the daughter molecules consisting of each one strand of the parental DNA molecule as well as one strand of the copied DNA molecule. After the second replication cycle two of the DNA molecules will exists in the same formation as the daughter molecules, whilst the remaining two while consists entirely of copied DNA strands, as shown in the model given.

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The theory of dispersive replication suggests, that the parental DNA molecule replicates, distributing random quantities of material into two daughter molecules. This causes the daughter molecules to consist of fragments of both parental as well as replica DNA as seen in the model given. The model shows a symmetrical outcome, however various distributions were theorized.

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The Meselson-Stahl experiment was named after the two scientists, Meselson and Stahl who conducted the subjected experiment in 1958. They constructed their experiment on the replication of E. coli, which is known to be a fast replicator (merely 20 minutes for one cycle in optimal condition). An essential part of this experiment was their decision to incorporate heavy nitrogen-n15 into the parental DNA molecule of the E. coli to distinguish it from the later generations, which they subjected to n14 or light, natural nitrogen. They embarked on this process by letting the parental DNA go through multiple replication processes in a n15 containing medium. This resulted in the incorporation of n15 into the primary DNA or parental DNA molecule. The secondary process they conducted was the subjection of the parental DNA molecules to a n14 or light nitrogen consisting medium. What made this experiment very efficient was the usage of density-gradient centrifugation. Which meant, in this case, the observance of the settling of heavy nitrogen at a lower height level than the light nitrogen due to their density. Meseleson and Stahl primarily observed the density-gradient centrifugation of solely the n15 E. coli. As expected, the heavy nitrogen settled at the bottom. Secondly, they put the n15 E. coli mixed into the n14 consisting medium through this process and observed heavy nitrogen settling at the bottom as well as a mixture of n15 and n14 above the n15 E. coli. Finally they repeated this process after a longer period of E. coli replication in the n14 consisting medium, resulting in more generations of replication of DNA molecule subjected to this experiment. What they found were three different levels: the n15 consisting E. coli (parental DNA) the n15 and n14 consisting E. coli (mixture) and a level consisting solely of n14 (100% light nitrogen DNA molecules), above the previously mentioned.