Uses the PCR primase

to directory mode

The DNA polymerase

The polymerase chain reaction is based on a reaction catalyzed by DNA polymerase I. DNA polymerases are important enzymes in cellular processes that are responsible for DNA duplication and the repair of the DNA strand.

Polymerases use a single-stranded DNA template to synthesize the opposite strand until a double-stranded DNA molecule has emerged again. These enzymes not only ensure identical duplication, but also close gaps in the DNA that have arisen, for example, from UV radiation or chemicals. The substrate for the DNA polymerases are nucleotide triphosphates; pyrophosphate (diphosphate) is released during the condensation reaction. In most cases, DNA polymerases require magnesium ions as a cofactor.

Different DNA polymerases with different properties exist in the cell. The actual task of DNA polymerase I in the cell is to repair copy errors or damage in the DNA. This enzyme cannot start a new DNA strand, but requires, in addition to an intact parent strand, a free 3'-OH in the gap in the opposite strand. In the PCR, the primer with its free 3'-OH end takes over the function of the opposite strand. The synthesis therefore only ever proceeds in one direction, the 5'-3 'direction.

In addition to the polymerase enzyme activity, many DNA polymerases have a correction function (proofreadingActivity), i.e. they recognize whether they have incorporated the wrong nucleotide in the DNA and can cut it out again immediately (3'-5'-exonuclease activity). Some polymerases also have a 5'-3 'exonuclease activity with which they can break down an old, existing DNA strand in the direction of synthesis.