Class 12 Biology Molecular Basis of Inheritance Machinery & Enzymes for Replication

Machinery & Enzymes for Replication

Enzymes play an important role acting as catalysts during the process of DNA replication. Some of the important enzymes are:

  • DNA polymerase
  • Helicase
  • Primase
  • DNA ligase

Energy source is needed to provide energy during the replication process. Deoxyribonucleoside triphosphates act as substrates & provide energy for polymerization reaction.


DNA polymerase

DNA polymerase creates DNA from nucleotides. It reads the existing DNA strands to create two new strands that match the existing ones. This enzyme is needed every time a cell divides so that one copy of DNA can be passed to each daughter cell.

DNA polymerase is a highly efficient enzyme, as it can replicate a large number of base pairs in a very short time. Rate of replication or Rate of polymerization is approx 2000 bp per second. A total of 4.6 * 106 base pairs are replicated within 18 minutes.  DNA polymerase also catalyze with high degree of accuracy. A mistake is made once in every 1 billion base pairs copied. DNA polymerase proof reads to check for errors. However, these errors if remain can cause mutations.


Enzyme Helicase unwinds DNA from tightly double stranded structure. Only after the strands are separated, DNA polymerase can do its job of creating the new strands. This enzyme separates the strands by breaking the hydrogen bonds between the bases of the two strands.



This enzyme creates a short fragment of RNA (primer) paired with the template DNA strand. This enzyme initiates the process of creation of new strands. DNA polymerase cannot initiate the process on its own. Therefore, primase initiates the same.

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