Final answer:
The experimental basis for semiconservative DNA replication was shown in the Meselson-Stahl experiment. DNA synthesis occurs under the direction of DNA pol 3 and not DNA pol 1. In vivo synthesis occurs in the 5' to 3' direction. DNA synthesis is discontinuous on the lagging strand, as shown by the discovery of Okazaki fragments.
Step-by-step explanation:
The experimental basis for concluding that DNA replicates semiconservatively in prokaryotes and eukaryotes is the famous Meselson-Stahl experiment. They used heavy isotope labeling of DNA and showed that after one round of DNA replication, the resulting DNA consisted of one heavy-labeled strand and one light strand. This supported the idea of semiconservative replication.
It was demonstrated that DNA synthesis occurs under the direction of DNA pol 3 and not DNA pol 1 by isolating mutants of these enzymes in E. coli. They found that mutants deficient in DNA pol 1 were still able to replicate DNA, while mutants deficient in DNA pol 3 were unable to carry out DNA replication.
In vivo synthesis occurs in the 5' to 3' direction because DNA polymerase can only add nucleotides to the 3' OH end. Therefore, DNA is extended in the 5' to 3' direction.
The discontinuous synthesis of one of the two template strands was demonstrated through the discovery of Okazaki fragments. These fragments are short pieces of DNA that are synthesized on the lagging strand during DNA replication. They are the result of the discontinuous DNA synthesis that occurs on the lagging strand.