Elementary plant Biochemistry and Biotechnology (2+1)

Meselson-Stahl Experiment: Proof for Semiconservative DNA replication

• In 1958, Mathew Meselson and Franklin Stahl showed that the replication of bacterial chromosomal DNA was semi conservative. E. coli were grown for many generations in a medium containing 15 N so that, their DNA became universally labeled with the isotope (heavy DNA).
• The cells were then shifted to a medium containing normal 14N and DNA was isolated from cells after one and two rounds of replication.
  
• The DNA was analyzed by buoyant density centrifugation, which discriminates between heavy DNA and normal light DNA and intermediate DNA containing one heavy strand and one light strand.
  
• After one round of replication, the DNA was all of intermediate density and after two, there were equal amounts of intermediate density and light DNA (Fig). Thus, this experiment proved that cellular genomes replicate semi conservatively.