DNA Replication | Molecular basis of Inheritance | Class 12 Biology | NEET & CUET

DNA Replication
In the process of DNA replication, the DNA makes multiple copies of itself. It is a biological polymerisation, which proceeds in the sequence of initiation, elongation, and termination. It is an enzyme-catalysed reaction. DNA Polymerase is the main enzyme in the replication process.
DNA Replication Steps
Following are the important steps involved in DNA replication:

Initiation
DNA replication demands a high degree of accuracy because even a minute mistake would result in mutations. Thus, replication cannot initiate randomly at any point in DNA.

For the replication to begin there is a particular region called the origin of replication. This is the point where the replication originates. Replication begins with the spotting of this origin followed by the unwinding of the two DNA strands.

Unzipping of DNA strands in their entire length is not feasible due to high energy input. Hence, first, a replication fork is created catalysed by the helicase enzyme, which unzips the DNA strand.

Elongation
As the strands are separated, the polymerase enzymes start synthesising the complementary sequence in each of the strands. The parental strands will act as a template for newly synthesising daughter strands.

It is to be noted that elongation is unidirectional i.e. DNA is always polymerised only in the 5′ to 3′ direction. Therefore, in one strand (the template 3‘→5‘) it is continuous, hence called continuous replication while on the other strand (the template 5‘→3‘) it is discontinuous replication. They occur as fragments called Okazaki fragments. The enzyme called DNA ligase joins them later.
Termination
Termination of replication occurs in different ways in different organisms. In E.coli like organisms, chromosomes are circular. And this happens when the two replication forks between the two terminals meet each other.

#neet #biology #cuet #class12