Dispersive neither parental molecule remains in tact; both chains of each replicated double helix contain old and new segments. 1958 meselson and stahl: bacteria was grown for several generations in an n15 (heavy) medium. The heavy isotope, n15 has one more neutron in its nucleus than the normal. N14 isotope: the heavy isotope was incorporated into the nitrogenous bases of dna, resulting in the entire dna being labeled with n15, after transferring the bacteria into a medium containing light n14 isotopes, the new. Dna polymerase is the primary enzymes of dna replication. Dna of different densities separated into bands, with the densest dna settling closer to the bottom of the tube. During replication, complimentary polynucleotides chains are assembled from individual deoxyribonucleotides by enzymes known as dna polymerase. Deoxyribonucleoside triphosphates are the substrates for the polymerization reaction catalyzed by. Dna polymerase catalyzes the assembly of a new dna strand that is complimentary to the template strand.