Final answer:
The Meselson and Stahl experiments aimed to understand how DNA replicates, and they demonstrated that DNA replication is semi-conservative, with each new DNA molecule containing one original and one new strand.
Step-by-step explanation:
The primary purpose of the Meselson and Stahl experiments was to determine how DNA replicates.
In 1958, Matthew Meselson and Franklin Stahl set out to understand the mechanism of DNA replication. They used E. coli bacteria, growing them in a medium containing a heavy isotope of nitrogen, 15N, which gets incorporated into their DNA. After several generations, they transferred the bacteria to a medium with the normal 14N isotope. They then extracted the DNA from cells and utilized density gradient ultracentrifugation to separate DNA based on its density.
Their findings showed that after one generation, the DNA extracted had an intermediate density, suggesting each DNA molecule was composed of one old (heavy) and one new (light) strand, indicating semi-conservative replication. Further generations produced a mix of intermediate density DNA and light DNA, conclusively supporting the semi-conservative replication model, where each new DNA molecule consists of one strand from the original molecule and one newly synthesized strand.