Meleson and Stahl's experiment

• 1. two samples of bacteria grown - one in a nutrient broth containing light nitrogen and one in a nutrient broth containing heavy nitrogen. as the bacteria reproduced, they TOOK UP NITROGEN from the broth to HELP MAKE NUCLEOTIDES FOR NEW DNA. So the nitrogen GRADUALLY BECAME PART of the bacteria's DNA
• 2. A sample of DNA taken from each batch of bacteria and SPUN IN A CENTRIFUGE. The DNA from heavy nitrogen broth settled lower down the centrifuge tube than from the light nitrogen broth- BECAUSE IT IS HEAVIER
• 3. The bacteria grown in the heavy nitrogen broth were taken out and put in a broth containing ONLY LIGHT NITROGEN. The bacteria were left for one round of DNA replication and then another DNA sample was taken out and spun in the CENTRIFUGE
• 4. IF REPLICATION WAS CONSERVATIVE, the original heavy DNA , which would still be together, would settle at the bottom and the new light DNA would settle at the top.
• 5. if replication was semi-conservative, the new bacterial DNA molecules would contain 1 strand of old DNA (containing heavy nitrogen) and one strand of new DNA (containing light nitrogen) . So the DNA would settle out BETWEEN where the light and heavy nitrogen settled out
• 6. As it turned out the DNA settled out in the middle which showed that the DNA molecules contained a mixture of heavy and light nitrogen. The bacterial DNA had replicated semi-conservatively in the light nitrogen
• what did other scientists do once meselson and stahl had confirmed that DNA replication in bacteria was semi-conservative?

  Other scientists carried out experiments to show that it was the universal method for DNA replication in all living things