At DNA replication forks, the overall growth of the antiparallel two daughter DNA chains appears to occur 5'-to-3' direction in the leading-strand and 3'-to-5' direction in the lagging-strand using enzyme system only able to elongate 5'-to-3' direction, and I describe in this review how we have analyzed and proved the lagging strand multistep synthesis reactions, called Discontinuous Replication Mechanism, which involve short RNA primer synthesis, primer-dependent short DNA chains (Okazaki fragments) synthesis, primer removal from the Okazaki fragments and gap filling between Okazaki fragments by RNase H and DNA polymerase I, and long lagging strand formation by joining between Okazaki fragments with DNA ligase.