Initiation of DNA Replication

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There are three steps that involved in DNA replication which are initiation, elongation, and termination. DNA replication is initiated from fixed origins which include repeated sequences. Besides, DNA double helix needs to unwind DNA replication in E.coli will use some protein and enzyme which help in DNA replication such as DNA gyrase, helicase, single-strand DNA binding proteins, and primase. DNA gyrase plays an important role for unwinding supercoils in DNA before started the DNA replication. For initiation of replication, other things that essential are a Nucleotide sequence that binds to initiation proteins and a primer which can be extended with the help of DNA polymerase by adding nucleotides[1]. First and foremost, the chromosome of E.coli has the single origin of replication which has 245 base pairs. Most of the base pairs are A/T because there is less hydrogen bond which is only 2 hydrogen bond held together between A/T base pair indirectly DNA strands will able to separate easily.

The initiation of DNA replication will be started by the enzyme helicase. Enzyme helicase binds to the DNA sequence which is the origins, thus, it causes the DNA double helix to unwind. When the DNA double helix unwinds, it destroys the hydrogen bond between the complementary nitrogenous bases pair. Then, each DNA separated strand become the template for the using of DNA replication[2]. Single-strand DNA binding protein is added to prevent single strand from rewinding.


  1. Mathews et al. 2000. Biochemistry. 3rd Edition. Benjamin Cummings. Pg 909.
  2. Molecular mechanism of DNA replication. Khan Academy. 2018 [cited 24/11/2018]; Available from:
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