[General process of aging]

Genetic instability is considered to be a fundamental factor in the ageing process. This instability results from the accumulation of damage caused to DNA, and this is demonstrated by the relationship between longevity and DNA repair. However, the accumulation of simple somatic mutations does not explain all the experimental findings. We are forced to take into account, not only the instability of the genes, but also the instability of the expression of the genes. Knowing that the expression of genes depends on interactions between DNA and proteins, we can see that genetic instability is based, at least in part, on protein synthesis. Attention has recently been drawn to the mechanism of transcription and notably of messenger DNA division. At the level of translation, the rate at which messenger DNA is degraded and various elongation factors necessary for ribosome activity have also been implicated. Post-translational changes of proteins by glycosylation or oxidation may be involved in the progressive accumulation of errors, which finally leads to cell death.