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, showing that the transcription activity of genes is gradually lost in an orderly manner, prompting cells and tissues to undergo progressive and regular phenotypic changes and even aging and death.
Biologically speaking, aging is a spontaneous and inevitable process of organisms with the passage of time. It is a complex natural phenomenon, which is manifested in the decline of structure and function, and the decline of adaptability and resistance. Physiologically, aging is regarded as an individual development history from fertilized eggs to old age. Pathologically, aging is the result of stress and strain, injury and infection, immune response decline, malnutrition, metabolic disorders, negligence and abuse.