Question

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

Answer 1

DNA replication occurs in small replication forks. It does not occur in its entire length in one time as DNA is a very large molecule and only that part of DNA opens up which is being replicated. The opening of the whole DNA molecule would be an energetically more expensive process.  

The main enzyme involved in DNA replication is the DNA-dependent DNA polymerase. This enzyme catalyzes the polymerization of deoxynucleotides along with the 5'→ 3' direction, and hence, replication is continuous along the 3'→ 5' strand (leading strand) and discontinuous along with the template, i.e., the 5'→ 3'  direction (lagging strand).  

Okazaki fragments are short DNA segments on the lagging strand, formed in the 5'− 3'  direction, starting from RNA primers. A separate RNA primer is needed for the synthesis of each Okazaki fragment. These discontinuously synthesized fragments are later joined by the enzyme DNA ligase. 

Ori stands for Origin of replication. This site has a highly conserved sequence of DNA among various species. The replication of DNA starts here because this site attracts some proteins which help in the opening and unwinding of DNA and this leads to the initiation of replication.  

The function of DNA Ligase is to join the two nucleotides. During the DNA replication process, it joins the Okazaki fragments of the daughter DNA to form the complete DNA molecule on the lagging strand.