The mechanism of DNA replication

As Meselson and Stahl demonstrated in their experiment, DNA replication happens by a semi-conservative mechanism.

DNA helicase breaks the hydrogen bonds holding the two polynucleotide chains together. The area where the helicase works is a ‘replication fork’.

DNA polymerase joins new nucleotides to their complementary bases by catalysing the formation of phosphodiester bonds between the deoxyribose and phosphate groups working from the 5’ to 3’ direction. The original polynucleotide chains act as a template for the aligning of new nucleotides.