Question

In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" nitrogen (^15 N) and then transferred the bacteria to a medium containing^14 N ("lighter" nitrogen) and allowed some of the the bacteria to undergo one round of replication and some bacteria to undergo two rounds of replication. They then performed density gradient centrifugation and looked to see where the DNA settled in the test tube. In the diagram below, draw bands indicating the density of the DNA before replication, after one round of replication and after two rounds of replication. The above represent the actual results from Meselson and Stahl's experiment. What would the results have looked like if replication were conservative instead of semiconservative?

Answer 1

:ZL Z179/0ZOZ SEMI- CONSERVATIVE REPLICATION V DNA tomos Son 14 15 NN's Hybrid wccccx T DNA DMA No-N14 Hybrid Before Replication After one wound of Replication Hybrid After two wunds of replication CONSERVATIVE REPLICATION NDRA + wooled Dooood NI4_Nis Hybrid DNA z Sassar N14 + N14 N's DIVA Xooma asash ganessa Before NIS Replication After one round of After two rounds of replication replication

In semi-conservative replication, each strand of parent DNA (N15) acts a template for the synthesis of its complementary strand (N14) and is integrated into the daughter DNA double helix to produce a N15-N14 hybrid DNA.

But in the conservative replication, the parent DNA strands (N15) act as templates but are not integrated into the daughter strands (N14). They produce two DNA duplexes, one with two original strands and another with two newly synthesized strands.