Question

The Meselson-Stahl experiment proved that DNA undergoes semiconservative replication in E.coli.

a. Explain conservative, semiconservative and dispersive replication. Also, if A new strain of Alien bacteria has just been discovered. Their genetic material is very similar to DNA, however it undergoes dispersive replication. What would be observed in the Meselson-Stahl experiment with the Alien DNA?

Answer 1

Ans:

Conservative replication: The replication in which two newly synthesized strands obtained by replication of DNA molecule would associate to form one duble helix, while the two old strands would remain together as one double helix, then it is called consevative replication. In conservative replication, parental strand are fully preserved. If the E. coli cells were initially grown on heavy medium (15N) and then transferred to light medium (14N). After one generation in conservative replication, they are produce Half heavy (15N) and half light DNA (14N) in CSCl equilibrium density gradient, no hybrid DNA are produce. After two generation on light medium, they are produce heavy and light DNA but the intensity of light DNA is more than heavy DNA.

Semiconservative replication: The replication in which the two strand of DNA is separated and each strand serve as a template and each newly synthesized DNA double helix contain one parental strand and one new strand, then it is called semiconsevative replication. So, parental strand are half preserved. If the cells grown on heavy medium (15N), are transferred to light medium (14N). After one generation they are produce hybrid DNA (15N- 14N). After two generation on light medium, they are produce hybrid DNA (15N- 14N) and light DNA (14N).

Dispersive replication: The replication in which the two strand of DNA double helix first cuts into pieces, each fragments would replicate and then rejoin; each progeny molecule would have old and new segments along its length, then it is called dispersive replication So, parental strand are not preserved. If the cells grown on heavy medium (15N), are transferred to light medium (14N). After one generation they are produce hybrid DNA (15N- 14N) and after two generation on light medium, they are produce hybrid DNA (15N- 14N).

If the alien DNA shows dispersive replication, then it produces a patchwork of heavy and light DNA in the Meselson-Stahl experiment after replication. If the alien bacterial cells with alien DNA grown on heavy medium (15N) and then are transferred to light medium (14N), after one generation they are produce hybrid DNA (15N- 14N).