Replication of DNA

Replication of DNA

DNA replication means synthesis of DNA.It occurs during the S-phase (synthesis phase) of cell cycle. DNA molecule performs 2 major functions i.e   Autocatalytic  function and Heterocatalytic function.

Whenever a DNA molecule synthesizes another DNA molecule similar to  it at that time it is called autocatalytic function. It is the replication of DNA.But whenever the DNA molecule directs the synthesis of protein, dissimilar in structure compared  to its own structure involving different types of RNAs it is called heterocatalytic function.

There are three possible ways of DNA replication i.e Dispersive,Conservative and Semiconservative.In the dispersive and conservative methods of DNA replication there is no experinmental proof available. In dispersive method of replication the two strands of mother DNA break at several points resulting in several pieces of  DNA.Each piece replicates and pieces are reunited randomly ,so the 2 copies of DNA  molecules are formed from single copy The new DNA molecules are hybrid which have  old and new DNA in patches .In conservative method of replication two DNA molecules are formed. One molecule has both parental strands and the other contains both newly synthesized strands.

Semiconservative method of DNA replication was proposed by Watson and Crick.It  states at the time of DNA replication the two parental strands are seperated.

Then opposite to each of the parental strand a new strand a new strand is synthesized.At this time the separated parental strand serves as a template or guide or model for the formation of new but  complementary strand.So at the end of the DNA replication  from a parent DNA molecule. Two daughter  DNAs  are synthesized where each one contains one parental strand or old strand and other newly formed complementary strand.

This semiconservative mode of DNA replication was experimentally proved by Meselson  and stahl in 1958, from E.coli.