In this chapter, we focused on how DNA is replicated and synthesized. We also discussed recombination at the DNA level. Along the way, we encountered many opportunities to consider how this information was acquired. On the basis of these discussions, what answers would you propose to the following fundamental questions? What is the experimental basis for concluding that DNA replicates semiconservatively in both bacteria and eukaryotes?

Key Concepts

Semiconservative Replication

Semiconservative replication is the process by which DNA is copied, resulting in two DNA molecules, each containing one original strand and one newly synthesized strand. This model was established through experiments, notably the Meselson-Stahl experiment, which demonstrated that after replication, the DNA strands consist of one old and one new strand, confirming the semiconservative nature of DNA replication.

Meselson-Stahl Experiment

The Meselson-Stahl experiment, conducted in 1958, used isotopes of nitrogen to trace the replication of DNA in E. coli. By growing bacteria in a medium containing heavy nitrogen (N-15) and then transferring them to a medium with light nitrogen (N-14), they were able to analyze the density of DNA after several generations, providing clear evidence for the semiconservative model of DNA replication.

DNA Replication in Bacteria and Eukaryotes

DNA replication occurs in both bacteria and eukaryotes, though the mechanisms and structures involved differ. In bacteria, replication begins at a single origin and proceeds bidirectionally, while eukaryotic replication involves multiple origins on each chromosome, with complex regulation and coordination. Understanding these processes is crucial for grasping how genetic information is accurately passed on during cell division.