INTRODUCTION
In bacterial (prokaryotic) cells such as E. coli, most or all of the DNA is in the form of a single, circular, double-stranded DNA molecule. In contrast, each unreplicated eukaryotic chromosome contains a single, linear, double-stranded molecule associated with at least as much protein (by mass) as DNA. This tutorial will examine replication of double-stranded DNA.

DNA replication is a complex process requiring a number of different enzymes. DNA replication is semiconservative, meaning that each daughter double helix contains one strand from the parent molecule and one newly synthesized strand. Completion of replication results in the formation of two daughter molecules, each containing one old and one newly synthesized strand.