Question

As a reminder, PCR is the technique used to replicate DNA in the lab. PCR is based on the way DNA is replicated in cells.

During PCR template DNA plus other ingredients are placed in a test tube and the solution goes through repeated cycles of heating and cooling. You can find more information about PCR here.

The 'ingredients' of a basic PCR reaction are: DNA template, primer, nucleotides, DNA polymerase, and any salts required for polymerase function (buffer).

No ligase is required in PCR but it is a necessary for DNA replication within the cell.

If DNA ligase is essential for DNA replication in a cell why isn't it necessary in PCR?

Hint: Think about what the role of ligase is normally in replication.

Answer 1

Ans- In the cell, DNA ligase is used for joining of discontinuous okazaki fragments. These fragments are not formed in PCR therefore, no DNA ligase is needed. The PCR amplifies particular segment of DNA i.e denatured in first step of PCR and the two primers are used forward primer that binds one of two strands and reverse primer binds another strand leading to synthesis of complete strands with no nicks. The two strands by complementarity then anneal to one another.