Chemistry of the Gene: Synthesis, Modification and Repair of DNA

All cells of a living organism possess the same quantity and quality of DNA. Since these cells res.ult from a single cell by successive cell divisions, a very precise mechanism for DNA synthesis (replication) should be available in the cell. This DNA is also variously modified to allow for the recognition of (i) old and newly synthesized strands of DNA duplex, (ii) any foreign DNA invading the cell or (iii) the active (expressed) and passive genes. There are also mechanisms for repair of DNA damage in the cell. In this section, details of the mechanism of DNA synthesis (particularly DNA directed DNA synthesis i.e. DNA replication and briefly also RNA directed DNA synthesis i.e. reverse transcription) along with a very brief account of DNA modification (methylation, etc.) and DNA repair will be presented.