Meselson-Stahl experiment

The Meselson-Stahl experiment was an experimentprove that DNA replication was semiconservative. Semiconservative replication means that whendouble stranded DNA helix was replicated, each oftwo double stranded DNA helices consistedone strand coming fromoriginal helixone newly synthesized.

Nitrogen ismajor constituentDNA,genetic materialall cells. Itcommonly found in¹⁴N isotope, butcan also be found inheavier ¹⁵N isotope.

E. coli were grownseveral generations inmedium¹⁵N. The DNA ofresuling cells hadhigher density (was heavier). After that, E. coli cellsonly ¹⁵Ntheir DNA were put back into¹⁴N mediumwere alloweddivide only once. DNA was then extracted fromcellwas comparedDNA from ¹⁴N DNA¹⁵N DNA. It was foundhave exactly an intermediate density. This supportedideasemiconservative replication.

The DNA was intermediatedensity becausehad an all ¹⁵N DNA strandan all ¹⁴N DNA strand. The all ¹⁵N strand was one oforiginal strands inoriginal cell. The all ¹⁴N strand wasnewly synthesized strand.

Trivia : Meselson's external advisorhis thesis was Richard Feynman. Feynman quotes this experiment as onehis reason'sstaying at Caltech. Feynman had just got an offer fromeast coastwas seriously debating going there when Meselson approached him withresultsthis experiment. Feynman thought thereno way this can happen anywhere else, so decidedstay!!