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A well-established example of bacterial aging is Caulobacter crescentus.This bacterium begins its life as a motile swarmer cell. Once it has found a suitable substrate, the swarmer cell will differentiate into a non-motile stalked cell.The asymmetrically dividing cells then show signs of detrimental genetic variation as they divide. [9]
Senescence (/ s ɪ ˈ n ɛ s ə n s /) or biological aging is the gradual deterioration of functional characteristics in living organisms. Whole organism senescence involves an increase in death rates or a decrease in fecundity with increasing age, at least in the later part of an organism's life cycle .
Why does biological aging occur? There are a number of hypotheses as to why senescence occurs including those that it is programmed by gene expression changes and that it is the accumulative damage of biological structures, particularly damage to DNA .
The two theories; non-adaptive, and adaptive, are used to explain the evolution of senescence, which is the decline in reproduction with age. [8] The non-adaptive theory assumes that the evolutionary deterioration of human age occurs as a result of accumulation of deleterious mutations in the germline. [8]
Biological immortality (sometimes referred to as bio-indefinite mortality) is a state in which the rate of mortality from senescence (or aging) is stable or decreasing, thus decoupling it from chronological age. Various unicellular and multicellular species, including some vertebrates, achieve this state either throughout their existence or ...
Senescence and SASP can also occur in post-mitotic cells, notably neurons. [12] The SASP in senescent neurons can vary according to cell type, the initiator of senescence, and the stage of senescence. [12] An online SASP Atlas serves as a guide to the various types of SASP. [8]
The human skull is used universally as a symbol of death. [1] Death is the end of life; the irreversible cessation of all biological functions that sustain a living organism. [2] The remains of a former organism normally begin to decompose shortly after death. [3] Death eventually and inevitably occurs in all organisms.
The typical normal human fetal cell will divide between 50 and 70 times before experiencing senescence. As the cell divides, the telomeres on the ends of chromosomes shorten. The Hayflick limit is the limit on cell replication imposed by the shortening of telomeres with each division. This end stage is known as cellular senescence.