Abstract
Aging can be defined as progressive and irreversible loss of vitality and increasing mortality coming inescapably with age. It is a stochastic process, rather than a program.
The biochemical essence of aging lies in impossibility to prevent accumulation of random errors in important biomolecules, such as DNA and proteins. In the complicated process of aging, there are roles for reactive oxygen species, mitochondrial dysfunction, reactive carbonyls, and damage to genomic DNA including telomeres, epigenetic alterations, cell senescence, and collapse of proteostasis.
Although all tissues of human body age, the biological limits of maintenance and repair affect the non-dividing cells the most. As the key organs of human body, brain, heart, and skeletal muscle, are based on postmitotic cells, a human being in his biological body can never reach immortality.
Within the biological limits, organisms are equipped with important adaptable mechanisms for body maintenance and repair, such as stress-induced cellular resistance to stress (hormesis), autophagy and DNA damage response. Insight into these mechanisms provides rationale for benefits of life style interventions, such as caloric restriction and physical exercise, and in future might even bring drugs that could slow aging.