PLEASE ANSWER ALL PARTS FULLY! How did the Meselson & Stahl’s experiment allow the investigators to...

PLEASE ANSWER ALL PARTS FULLY!

How did the Meselson & Stahl’s experiment allow the investigators to distinguish between the 3 overall methods of DNA replication? What approaches were used in investigating the enzymology of DNA replication, remembering that studying an essential function presents a particular challenge?

Expert Solution

Meselson & Stahl’s experiment allow the investigators to distinguish between the 3 overall methods of DNA replication. The three hypothesis for overall methods of DNA replication are as given below

Semiconservative hypothesis:- This was proposed by Watson and Creek. According to this method the two strands of a DNA molecule separate during replication and each strand then acts as a template.

Conservative hypothesis:- According to this method, the entire DNA molecule acts as a template for the synthesis of new DNA molecule.

Dispersive hypothesis:- This was proposed by Max Delbrück, This method suggest that unwinding the two strands of the double helix occurs by breaking the DNA backbone every 10 nucleotides. The DNA then gets untwisted and attaches the old strand to the end of the newly synthesized one.

Meselson and Stahl’s made use of ¹⁵N to track the replication process. The process that helped understanding the 3 methods is as follows.

In an experiment, E. coli was allowed to grow on medium containing NH4Cl with 15N. Over several generation, 15N got incorporated in the Ecoli DNA. The density of 15N DNA was greater than 14N DNA. Thus, E.coli with 15N DNA was separated and was allowed to grow on 14N medium. The growth of these cells was observed by microscopic cell counts and colony assay.

DNA was extracted periodically and was compared to pure 14N DNA and 15N DNA. After one replication, the DNA was found to have intermediate density.

According to conservative method of DNA replication, equal amounts of DNA of the higher and lower densities would be observed and not the DNA with intermediate density. Hence, the conservative method of DNA replication was excluded.

Intermediate density DNA would be observed in both semi-conservative as well as dispersive methods of replication.

The experiment was further continued upto two replications. After two replications, equal amounts of DNA one with intermediate density and other with lighter density were observed. dispersive replication would have resulted in a single density. Thus, the results were inconsistent with dispersive method but were consistent with the semiconservative replication method.

Thus, Meselson & Stahl’s experiment allow the investigators to distinguish between the 3 overall methods of DNA replication.

gladiator answered 1 year ago

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