Evidence for semi-conservative replication

Replication is the making of a copy of DNA. Two ways are possible :

: conservative replication hypothesis (Click on the image to expand) : one daughter molecule contains both parent polynucleotides, and the other daughter molecule contains both newly synthesised strands.

: semi-conservative replication hypothesis. (Click on the image to expand) : in which both daughter molecules contain one polynucleotide from the original molecule and one newly synthesised strand.

A third hypothesis : dispersive replication in which each strand of each daughter molecule is composed partially of the original polynucleotide and partially of newly synthesised polynucleotide.

Two experiments were needed to establish the right mechanism :

1) The Meselson and Stahl experiment

2) A chromosome verification

The Crick and Watson Model of replication

Crick and Watson model of the double helix for DNA suggests a method by which replication may occur. The hydrogen bonds between the strands are broken and the molecule unwinds. Each strand can therefore act as a template to copy the DNA. Complementary nucleotides would then assemble, and the sugar phosphate backbone form by a condensation reaction.