What is DNA replication?

What are The Steps?

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The process by which DNA duplicates itself prior to cell division is called DNA replication.

What is DNA replication?

"Unzipping" the DNA double helix structure is the initial step in the replication process.

In this process, an enzyme called helicase is responsible for dissolving the covalent connections between DNA's complementary bases (A with T, C with G).

A replication 'fork' is the 'Y' shape formed when two single DNA strands separate during replication. The new DNA strands will be made using the original two strands as moulds.

One of the strands is "leading" since it is orientated 3' to 5' (toward the replication fork). The lagging strand has a 5'-to-3' orientation (away from the replication fork). Since the two strands are copied in opposite directions, the results are distinct: Leading Strand and Lagging strand

Leading Strand

First, an enzyme called primase generates a short RNA fragment called a primer, which binds to the 3' end of the leading strand. The primer is the first step in the DNA synthesis process.

DNA polymerase 'walks' along a DNA strand, adding new complementary nucleotide bases (A, C, G, and T) from the 5' end to the 3' end.

The term "continuous replication" is used to describe this type of copying. 

The primase enzyme generates many different RNA primers, which bind at different locations along the lagging strand.

Lagging strand

Okazaki fragments, chunks of DNA, are then grafted onto the trailing strand in the 5' to 3' orientation.

An enzyme called exonuclease removes the primer once the bases have been correctly paired (A with T, C with G) (s). Additional complementary nucleotides fill in the spaces left by the primer(s).

To ensure that the new DNA sequence is error-free, the new strand is proofread.

When DNA replicates, it creates two identical molecules, one with a new chain of nucleotides and the other with the original chain. This is why we say that DNA replication is "semi-conservative"; while half of the replicated chain comes from the original DNA molecule, the other half is completely novel.

Replicated DNA immediately reforms into a double helix shape.