Question

Explain Messelson and Stahl experiment. ​

Answer 1

Measelson And Stahl Experiment

• Measelson and Stahl (1958) demonstrated the semi-conservative mode of replication in E.coli.

• In this experiment E.coli was culture in a medium containing nitrogen salt labelled with heavy or stable isotope of N15 ( the common isotope of nitrogen is N14 (NH4Cl).

• The N15 was incorporated in both strands of DNA of E. coli and thus DNA becomes heavier, this DNA is called heavier DNA.

• Another preparation was also made in which E.coli was cultured in medium containing N14.

• N14 was also incorporated in both stands of DNA of E.coli.

• This DNA was lighter than the DNA of E.coli grown in N15 medium.

• The heavier and lighter DNA can be separated by Ceasium chloride density gradient ultracentrifugation.