Question

In PCR, a DNA polymerase is used in vitro to replicate a specific stretch of DNA within a DNA sample. However, none of the other proteins involved in DNA replication in vivo are needed. List the other proteins that are required for DNA replication in a living cell, and for each, explain why it does not need to be included in a PCR reaction.

Answer 1

Answer:

See the answer below

Explanation:

Apart from DNA polymerase, other enzymes (proteins) that are required for DNA replication in a living cell include:

• Helicase
• Primase
• Ligase; and
• Gyrase

The helicase enzyme functions to unwind the double helix structure of the DNA during replication. This enzyme is not needed in the PCR because only a  specific stretch of a single strand DNA is needed.

The primase enzyme functions to synthesize RNA primers during DNA replication. The required primer is added directly during PCR and this makes the use of the primase enzyme unnecessary.

The ligase enzyme functions to join the Okazaki fragments of the discontinuously replicated lagging strand of the DNA during replication. There is no leading nor lagging strand in PCR and replication of the target section of the DNA is done continuously. Hence, there is no need for the ligase enzyme.

The gyrase enzyme assists in the supercoiling of DNA strands that have been initially unwound during replication. Since only a stretch of DNA is utilized for PCR, no supercoiling is needed and, hence, no need for the gyrase enzyme.