Question

Describe DNA replication on the leading and lagging strands of DNA. Your answer must include a description of the roles of the following enzymes:

-DNA polymerase I (5’-3’polymerase activity, 3’-5’ exonuclease activity, 5’-3’ exonuclease activity)

​-DNA polymerase III (5’-3’polymerase activity, 3’-5’ exonuclease activity)

​-helicase, primase, ligase, gyrase

Answer 1

DNA replication is a process in which a DNA sequence is replicated from template
DNA. The process involves the functioning of various enzymes at various levels.
DNA replication in a given cell starts at specific locations in the cell known as origins of replication. In order to initiate the replication, firstly an enzyme called helicase is needed. Helicase unwinds the DNA double strands and makes
single template DNA strand available to the DNA polymerase.
Gyrase, an enzyme removes any strain during this unwinding process.
Primase gives the initial point for DNA polymerase to start the synthesis of nucleotides.
Now DNA polymerase III comes into the picture. This enzyme adds nucleotides complementary to the template strand
in 5' to 3' direction. This enzyme also proofreads if there is any mismatch in the
addition of nucleotides. DNA pol III can synthesize nucleotides in 5' to 3'
direction is known as the leading strand which is continuous.
But this is different from lagging strand as the synthesis is lagging and gaps present
in between these nucleotides and are filled with RNA primers in the process.
Later on these primers are removed and the DNA fragments are joined together and RNA
primers are replaced with DNA by an enzyme known as DNA ligase.