The replication

Polymerase, ligase, primer, primase, helicase ...

Before mitosis or meiosis can happen, a cell has to double its DNA. This happens through replication during the interphase.

Sequence of replication:

1. The enzyme topoisomerase unwinds the DNA double helix.

2. The helicase then splits the now enspiralized double strand of DNA into two single strands by dissolving the hydrogen bonds of the opposite base pairs under ATP consumption.

3. The primase synthesizes at the 3 'ends so-called primers, which are necessary for the beginning of the actual replication and serve as a starting point.

4. At the 3 'end of the primer, DNA polymerase begins to synthesize complementary bases, creating a new DNA duplex.

However, the DNA polymerase can only run from 5 'to 3'. As a result, the synthesis must proceed in the opposite direction on the antiparallel strand (3 'to 5'). And that only works if new primers are set again and again. In this way arise between the primers, single synthethisierte pieces of DNA, the so-called Okazaki fragments. One also speaks of a discontinuous formation of the DNA strand.

5. RNase H now removes the RNA primer from the DNA and another DNA polymerase closes the resulting gaps with complementary bases.

6. Finally, the enzyme ligase links the discontinuously formed strand through ester bonds.

As a result, two identical DNA strands have now emerged.

Proof of semiconservative replication

The Meselson-Stahl experiment to prove the semiconservative replication has its own article

Overview of enzymes and their activities

Topoisomerase: unwinds the double helix

Helicase: Opens the double helix

RNA primase: Synthetizers one piece of RNA (primer)

DNA Polymerase: Adds complementary nucleotides at the 3 'end

RNase H: removes RNA primer again from the newly synthesized DNA

DNA ligase: links the formed strands with ester bonds

Summary

The replication ensures a doubling of the DNA during the interphase

Replication is based on the principle of semiconservative replication

Enzymes (polymerases, primases, ligases, helicases) play an important role in doubling the DNA