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

Mechanism of DNA replication

Explanation:

• Mechanism of DNA replication:  

         i. Initiation –  

• There is a particular region called the origin of replication. This is the point where the replication originates.  

• The DNA strands are unwound to form a replication fork. This is created by polymerases enzyme which is an opening in the DNA strand.  

      ii. Elongation –  

• As the strands are separated, the polymerase enzymes start synthesizing the complementary sequence in each of the strands.  

• The parental strands will act as a template  

• Elongation is unidirectional i.e. DNA is always polymerized only in the 5′ to 3′ direction.

• 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  

• DNA ligase joins these fragments later on.  

       iii. Termination –  

• The termination 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. DNA - Ligase is the enzyme which glues the discontinuous .