This session will explain how DNA is replicated prior to cell division. In this process, DNA polymerase uses an original strand as a template to create a new daughter strand of DNA. Polymerization occurs in the 5' to 3' direction, creating a new strand that is anti-parallel to the original. Polymerization begins at a specific DNA sequence called the Origin of Replication and proceeds in two directions along both template strands. Because of the directionality of synthesis, one strand is synthesized continuously, while the other strand is synthesized in small fragments, which are then joined together by DNA ligase.

Learning Objectives

• To understand the semi-conservative model of DNA replication.
• To recognize the 5' and 3' ends of DNA and predict the direction in which replication will proceed.
• To predict the sequence of a newly synthesized strand of DNA, based on the sequence of the original strand.
• To identify the leading and lagging strands during replication.
• To understand the function of helicase and DNA ligase and explain why they are necessary.