Question

Explain the mechanism of DNA replication with the help of a replication fork. What role does the enzyme DNA-ligase play in a DNA replication fork?

Answer 1

The process of replication requires a set of enzymes. The main enzyme is DNA - dependent DNA polymerase, since, it uses DNA template to catalyse the polymerisation of deoxynucleotides these polymerase are highly efficient, fast and also catalyse the reaction with a high degree of accuracy. Any mistake during replication would result in mutations. Deoxyribonucleotides serve a dual purpose. In addition to acting as substrates, they provide energy for polymerisation of reaction.

For long DNA molecules, since the two strands of DNA cannot be separated in their entire length (due to high energy requirement the replication occurs within a small opening of the DNA helix, referred to as replication fork.

The DNA-dependent DNA polymerase catalyse polymerisation only in one direction 5'$\to$3'. This creates some additional complications at the replicating fork. Consequently, on one strand,( template with polarity 3'$\to$5'), replication does not initiate randomly at any one place, it starts at the origin of replication.

DNA ligase joins the discontinuously synthesised fragments by catalysing the formation of a phosphodiester bond.