With the passage of time, the degree of crosslinking is increasing, the consumption of active groups of biomolecules is decreasing, and the original molecular structure is gradually changing. The accumulation of these changes will gradually lead to the aging of biological tissues. On the one hand, these changes of biomolecules or genes will show gene products with different activities or even completely changed functions, on the other hand, they will also interfere with the recognition and binding of RNA polymerase, thus affecting the transcription activity, which is manifested in the orderly and gradual loss of gene transcription activity, prompting cells and tissues to undergo progressive and regular phenotypic changes, even aging and death.
Biologically speaking, aging is a spontaneous and inevitable process of organisms over time. It is a complex natural phenomenon, manifested in the decline of structure and function, and the decline of adaptability and resistance. Physiologically, aging is regarded as the individual development history from fertilized egg to old age. Pathologically speaking, aging is the result of stress and tension, injury and infection, decreased immune response, malnutrition, metabolic disorder, negligence and abuse.