It was purposed y Watson and Crick in 1953. It occurs in nucleus of the cell. This method is widely accepted method of DNA replication. In this replication, half of the original DNA molecules is conserved and complementary half is newly synthesized by base pairing. So, this method of replication is called semi-conservative replication.

Process of replication

1. Activation of nucleotides: The deoxyribonucleotides monophosphate such as dAMP ( Deoxy adenine monophosphate), dTMP, dGMP, dCMP occurs in nucleoplasm. These nucleotides are activated by enzyme phosphorylase to form deoxyribo nucleotide triphosphate by uniting with ATP (dATP, dTTP, dGTP, dCTP). This process is called phosphorylation.

2. Unwinding of DNA: Replication of DNA start at a specific point called initiation point. The two DNA molecules uncoil and separate due to breakage of hydrogen bonds between nitrogenous bases by an enzyme helicase.(The enzyme topoisomerase cut and rejoin one strand of DNA. In bacteria and virus , only one replication or initiation point is present because of which replication start and end at the same point. In Eukaryotes, the DNA molecules are large so it has many initiating point or replicon (over 1000 point).

3. Base pairing : Deoxyribonucleotide triphosphate pair with appropriate nitrogenous bases of templet DNA strand with the enzyme ligase (i.e., Adenine joint with Thymine and Cytosine joint with Guanine).

4. Conservation of triphosphate to mono phosphate : The deoxyribose nucleotide triphosphate molecules pair with nitrogenous bases of template strand change into Deoxy ribonucleotide monophosphate and release large amount of energy in the presence of enzyme pyrophosphatase.
5. Formation of new DNA Chain : the energy released by it is utilized in joining the adjacent nucleotides to form poly nucleotide chain by the enzyme polymerase.