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 Since the DNA strands are antiparallel, and replication proceeds in the 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.