DNA Replication

Introduction: As discussed previously, duplication or re-synthesis of genomic content is essential to maintain the life of an organism. DNA has to be precisely replicate to maintain the sequence identical to the parent DNA. It will protect the appearance of potential mutation and resulting changed phenotype. In the current lecture, we will discuss salient features of replication and underlying factors and mechanism.
Replication of a DNA fragment has to be performed keeping following point into the consideration.

1. The replication machinery must duplicate whole fragment.
2. The replication must be free of errors.
3. The machinery must amplify the fragment in a given time frame. For ex. replication has to be complete within the doubling time of an organism.

Replication Machinery: The replication of DNA required following enzymes and factors.

1. Primase: This enzyme synthesizes the primer at the site of replication to start the replication.

2. DNA Polymerase:  These enzymes are responsible for synthesis of DNA of pre-existing DNA fragment. These enzymes are incapable to perform denovo DNA synthesis but can be able to synthesize DNA on a pre-exisitng RNA or DNA primer. DNA polymerase has 3 different enzymatic activities; (1) 5´-3´ Polymerase, (2) 5´-3´ exonuclease and (3) 3´-5´ proofreading. E.Coli has 5 different DNA polymerase but only 3 are involved in replication and rest 2 are more involved in repair or recombination. Different properties of DNA polymerase is summarized in Table 27.1.