The first generation of bacteria was grown on a medium where the sole source of N was Nitrogen-15. Watson and Crick had predicted that DNA replication was semi-conservative. If it was, then the DNA produced by bacteria grown on light medium would be intermediate between heavy and light. Nucleotides have to be assembled and available in the nucleus, along with energy to make bonds between nucleotides. DNA polymerases unzip the helix by breaking the H-bonds between bases.
Prokaryotes open a single replication bubble, while eukaryotes have multiple bubbles.
The entire length of the DNA molecule is replicated as the bubbles meet. Image from W.H. Freeman and Sinauer Associates, used by permission. Since the DNA strands are antiparallel, and replication proceeds in thje 5' to 3' direction on EACH strand, one strand will form a continuous copy, while the other will form a series of short Okazaki fragments. Image from W.H. Freeman and Sinauer Associates, used by permission. A resource with graphics and other materials to augment molecular genetics.