How does DNA replication occur simply?
DNA molecule is like a twisted ladder. The horizontal bars are
made up of A-T, T-A, G-C,C-G. (A for Adenine, T for Thiamine, G for
guanine and C for Cytosine.) So if we brake the ladder
longitudinally, we have sequences of A, T, G, C, and corresponding
sequences of T,A,C,G on other half. So we can easily make two
copies.