DNA Polymerase

The process of DNA replication is made possible by the presence of an enzyme called DNA Polymerase. DNA replication gets started when DNA polymerase binds itself at a primer on one of the two strands of DNA. This single strand of DNA is then taken as the base or guide, often termed as a template, and DNA polymerase starts adding extra nucleotides as part of the replication process.

It is important to note that as of yet, genetic biologists do not know of any DNA polymerase that can start a new chain on its own. DNA polymerase always has to depend on an available 3’-OH group for adding the nucleotides.

As mentioned earlier in the article, DNA polymerase always looks for the presence of a primer where it can start adding nucleotides. This primer, which acts like a process starting cue, is composed of RNA and DNA bases and the sequence of these bases always has two RNA bases at the front. Enzymes called primase synthesize these RNA’s while it is the responsibility of helicase enzyme to form a single stranded structure of DNA from its double-stranded shape. It’s this new single stranded form that is then used to follow DNA replication process.

Some of the DNA polymerases are intelligent enough to exercise an error correction mechanism, which is a process of rectifying errors in the replicated DNA. In case a wrong pair of the base has been formed, the intelligent DNA polymerase recognizes it immediately and reverses the last pair in the replication process. This error correction process has also been named as Proofreading. After getting rid of the wrongly paired base, DNA polymerase restarts the replication process by adding a right pair of base nucleotides.

DNA polymerases have been classified as categories called families. These families are:

Family A: It consists of replicative as well as repair DNA polymerases.

Family B: Most of the polymerases in this family are of replicative nature and are known for their outstanding accuracy in the process.

Family C: These are bacterial chromosomal enzymes that are used in the replication process.

Family D: This family needs more research activities to be classified properly.

Family X: This family consists of some of the largely known eukaryotic polymerases.

Family Y: An interesting factor regarding DNA polymerases in Family Y is that they can work through damaged DNA and replicate it. However, depending on the circumstances, the error can either be escaped or worsened into mutation.

Family RT: These synthesize DNA by making use of an RNA template.