How does DNA replicate?
The process by which a cell copies its DNA is called DNA replication. Before DNA replication, a chromosome consists of one molecule of DNA. As replication begins, enzymes break the hydrogen bonds that hold the double helix together, and the two DNA strands unwind and separate. Another enzyme constructs primers which serve as an attachment point for DNA polymerase, the enzyme that assembles new strands of DNA. A primer base-pairs with a complementary strand of DNA. DNA polymerase attach to the hybridized primers and begin DNA synthesis. The enzyme DNA ligase seals any gaps, so the new DNA strands are continuous. Both of the strands of the parent molecule are copied at the same time. As each new DNA strand lengthens, it winds up with its template strand into a double helix. Semiconservative replication produces two copies of a DNA molecule, one strand is new and the other is parental.