What important discovery was made through the Meselson-Stahl experiment?

The Meselson-Stahl experiment provided pivotal evidence that DNA replication is semiconservative. This means that during the process of DNA replication, each of the two resulting DNA molecules consists of one original strand and one newly synthesized strand.

In their experiment, Matthew Meselson and Franklin Stahl used a technique involving density gradients to distinguish between the heavy and light isotopes of nitrogen incorporated into DNA. They labeled the DNA of Escherichia coli (E. coli) with heavy nitrogen (N-15) and then allowed the bacteria to replicate in a medium with lighter nitrogen (N-14). By extracting samples after different generations of replication and analyzing the density of the DNA, they were able to observe two distinct bands after one replication cycle, indicating that each DNA molecule contained one heavy and one light strand. After subsequent replications, they observed a consistent pattern confirming the semiconservative nature of DNA replication.

This discovery was crucial for understanding the mechanism of DNA replication and laid the foundation for modern molecular biology, as it clarified the process through which genetic information is passed on during cell division.