DNA replication is a fundamental biological process that creates exact copies of genetic material before cell division.
The Semi conservative model of DNA replication, proven by the landmark Meselson and Stahl experiment, demonstrates how each new DNA molecule contains one original strand and one newly synthesized strand. This model was revolutionary in understanding the steps of DNA replication, which occur in three main phases: initiation, elongation, and termination. During initiation, enzymes unwind the double helix at specific points called origin sites. The DNA replication enzymes including helicase, primase, and DNA polymerase work together to begin the copying process.
A crucial discovery in understanding DNA replication was made by Reiji and Tsuneko Okazaki in the 1960s. Okazaki fragments are short segments of DNA that form on the lagging strand during replication. These fragments are essential because DNA can only be synthesized in the 5' to 3' direction, requiring a discontinuous synthesis process on one strand. The role of Okazaki fragments in DNA synthesis involves creating these short pieces that are later joined together by DNA ligase to form a continuous strand. This process differs from the leading strand, which is synthesized continuously. The DNA replication diagram typically shows both the leading and lagging strands, with the lagging strand containing these characteristic Okazaki fragments. Understanding this process was crucial in establishing that DNA replication is semiconservative and semi discontinuous, meaning one strand is copied continuously while the other is copied in segments. This knowledge has been fundamental to our understanding of how genetic information is passed from one generation of cells to the next, and has important implications for fields like molecular biology and genetic engineering.
