DNA Replication and Enzymes
The first step of DNA replication is the unwinding of the double helix at specific points, called origins of replication. There may be hundreds or thousands of origins of replication in our DNA; however, there is usually only one in bacteria. The hydrogen bonds, mentioned earlier separate as enzymes catalyze the replication process. Adenine separates from thymine, and guanine separates from cytosine.
DNA primase, DNA polymerase and helicases are the main enzymes involved in DNA replication. The original DNA structure is unwound by helicases, at the origin of replication and each original single-stranded DNA molecule is used as a template. Single-stranded binding proteins then bind to the template to prevent degradation of the original DNA molecule.
DNA polymerase copies from the template and adds nucleotides from the 5’ end to the free 3’ end. As both ends of the double helix separate, Y-shaped regions result called replication forks. The two chains of the double helix are antiparallel so as nucleotides are added, there is a leading strand and a lagging strand - the two prongs of the fork.
The leading strand continually adds in the 5’ to 3’ direction along the template as DNA polymerase moves toward the replication fork. The lagging strand discontinually adds nucleotides to the template in small pieces called Okazaki fragments as DNA polymerase moves away from the replication fork.