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Chapter: Essentials of Anatomy and Physiology: Cell Structures and their Functions

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Cellular aspects of aging

List the major theories of aging.

Cellular aspects of aging

List the major theories of aging.

We are all familiar with the outward signs of aging, such as wrinkled skin, gray hair, and reduced vision. A number of cellular structures or events appear to be involved in causing these effects. The major hypotheses that attempt to explain how aging occurs concentrate on molecules within the cell, such as lipids, proteins, and nucleic acids. It is estimated that at least 35% of the factors affecting aging are genetic.

1.Cellular clock. One hypothesis of aging suggests the existence of a cellular clock that, after a certain passage of time or a certain number of cell divisions, results in the death of a given cell line.

2.Death genes. Another hypothesis suggests that there are “death genes,” which turn on late in life, or sometimes prematurely, causing cells to deteriorate and die.

3.DNA damage. Other hypotheses suggest that, through time, DNA is damaged, resulting in cell degeneration and death.

4.Free radicals. DNA is also susceptible to direct damage, resulting in mutations that may result in cellular dysfunctionand, ultimately, cell death. One of the major sources of DNA damage is apparently free radicals, which are atoms or molecules with an unpaired electron.

5.Mitochondrial damage. Mitochondrial DNA may be more sensitive to free-radical damage than is nuclear DNA. Mitochondrial DNA damage may result in loss of proteins critical to mitochondrial function. Because the mitochondria are the primary source of ATP, loss ofmitochondrial function could lead to the loss of energy critical to cell function and, ultimately, to cell death. One proposal suggests that reduced caloric intake may reduce free-radical damage to mitochondria.


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