Replication – the action in DNA 27th November 2023 – Tags: ,

Today we will try to introduce you to one of them – replication. When thinking about genetics, most of us think of the DNA helix. Two lines spinning around each other creating a screw-like shape. However, although genetics is actually based on genetic material in the form of DNA, many different processes are involved.

What is replication?

Broadly speaking, DNA replication is a process during which a copy of the genome is made in cells. In this process, DNA makes many copies of itself. DNA itself is a self-replicating structure that replicates semiconservatively. The replication process can be divided into three stages: initiation, elongation and termination. During each stage, various enzymes participate in the reaction. The most famous of them is DNA polymerase. During replication, each DNA chain serves as a template for the synthesis of a new chain.

DNA replication en
The diagram shows the entire replication process


The initiation process begins by attaching the appropriate protein at the replication initiation site. Under the influence of this protein, the DNA double helix unwinds on a small section. As a result of DNA unwinding, we obtain a characteristic structure called a replication eye or replication fork. In the eye area, subsequent proteins involved in further stages of replication begin to attach. The enzymes appearing during this stage are DNA helicase and DNA primase. Helicase unwinds the double helix, exposing the DNA strands, which will then be used in further stages. DNA primase acts as a stimulator for DNA polymerase.

Initiation of DNA replication
The diagram shows the replication initiation process. You can see the formation of replication forks.


At the beginning of this process, previously formed replication forks begin their journey in two opposite directions. The most important goal of this process is to obtain new DNA strands. Their formation requires an enzyme called DNA polymerase, which attaches free nucleotides to the 3′ end. At the very beginning of the strand there is a so-called primer, which is a short section of RNA produced by the enzyme primase. Thanks to this enzyme, an increasingly longer DNA strand called a replicon is created. The synthesis of the second strand, called the lagging strand, begins in the direction opposite to the direction of movement of the replication fork, i.e. from the 5′ end to the 3′ end. The extension of new DNA chains continues until the DNA molecule is completely copied.

DNA Polymerase DNA Replication
The diagram shows the elongation process, during which the DNA strand is further copied.


We can designate the formation of two daughter DNA molecules as the final moment of replication. We define it precisely when there is no more template DNA strand to copy, or when the replication forks meet and then end their operation. After DNA synthesis is completed, the newly synthesized strands are bound and stabilized. In the case of the lagging strand, two enzymes are needed to achieve the stabilization described – RNAase H, which removes the RNA primer at the beginning of each Okazaki fragment, and DNA ligase, which joins the fragments together to form one complete strand.

DNA replication
The diagram shows the location of the process and dates. We can see it marked with the letter T

All enzymes involved in replication:

  • DNA polymerase
  • DNA helicase
  • DNA primase
  • RNAase H
  • DNA ligase