Question

the experimental proof for semiconservative replication of dna was first shown in

Answer 1

The experimental proof for semi conservative replication of DNA was first shown in Escherichia coli. This was proved by Meselson-Stahl experiment. He began the experiment by growing E.coli in a medium or nutrition broth containing heavy  isotope of nitrogen. When bacteria was grown on a nutrition broth containing heavy isotope of nitrogen, it began to absorb the nitrogen and started using the absorbed nitrogen to synthesize new biological molecules including DNA. After many generations were grown in nutrition medium the nitrogenous bases were named with heavy $N^{15}$. The heavy DNA molecules were distinguished from normal DNA by Density gradient centrifugation and were transferred to medium containing $N^{14}$. As the cell multiplied the samples were collected at particular time intervals and  the DNA which remained as double helices were extracted. Various samples are separated independently on CsCl medium and the density of DNA is measured. The DNA extracted from the culture after one generation has intermediate density whereas the DNA extracted from another generation was composed of both in equal amounts.

Answer 2

The experimental proof for semiconservative replication of dna was first shown in Meselson-Stahl experiment in E. Coli bacteria.

The Meselson–Stahl experiment is an experiment by Matthew Meselson and Franklin Stahl in 1958 which supported Watson and Crick's hypothesis that DNA replication was semiconservative. In semiconservative replication, when the double stranded DNA helix is replicated, each of the two new double-stranded DNA helices consisted of one strand from the original helix and one newly synthesized. It has been called "the most beautiful experiment in biology." Meselson and Stahl decided the best way to tag the parent DNA would be to change one of the atoms in the parent DNA molecule. Since nitrogen is found in the nitrogenous bases of each nucleotide, they decided to use an isotope of nitrogen to distinguish between parent and newly copied DNA. The isotope of nitrogen had an extra neutron in the nucleus, which made it heavier.