Replication of DNA

Replication of DNA


  • DNA replication is a semi-conservative process, which means each of the two new DNA molecules comprises one original (conserved) strand and one newly synthesized strand.
  • The process occurs during the S-phase of the cell cycle to prepare for cell division.

Enzymes Involved

  • DNA helicase unwinds the original double-stranded DNA molecule by breaking hydrogen bonds between base pairs, creating the replication fork.
  • DNA polymerase synthesises a new strand of DNA in the 5’ to 3’ direction, using each original strand as a template.
  • DNA ligase seals any gaps between Okazaki fragments, short DNA sequences on the lagging strand.
  • RNA primase sets the starting point for replication by creating a short stretch of RNA called an RNA primer.
  • Topoisomerase prevents the DNA ahead of the replication fork from supercoiling.

Process of DNA Replication

  • Starts at specific points known as origins of replication.
  • The replication fork moves along the DNA, one strand is formed continuously (leading strand), while the other (lagging strand) is formed in fragments (Okazaki fragments).
  • The RNA primers are later removed and replaced with DNA by DNA polymerase.
  • DNA ligase then links the Okazaki fragments together on the lagging strand to ensure a continuous DNA sequence.

Proofreading and Repair

  • DNA polymerase verifies each new nucleotide against the template nucleotide; if they are incorrectly paired (a mistake known as a mismatch), it is removed.
  • DNA repair enzymes look for anomalies, such as bulges or nicks, and fix them before replication continues.
  • This comprehensive error-correction ensures DNA is replicated with high accuracy, and is vital for preventing mutations.


  • DNA replication ensures that every new cell has an accurate copy of the DNA from the parent cell, which is essential for maintaining the genetic identity of organisms and species.
  • Disruptions or errors in DNA replication can lead to mutations, which can cause diseases or developmental issues. Therefore, understanding DNA replication is key to understanding genetic disorders and potential treatments.