ABSTRACT
Mitochondria in liver cells of a centenarian are estimated to have divided by ssion (Figure 17.1) as many as 3600 times. It is clear that division acts to rejuvenate wornout parts of mitochondria that might otherwise decrease both energy output and ef- ciency. In Chapter 12 we discussed how specialized membranes of rhodopsin disks senesce on a timescale of days, and how tails of sperm cells, when exposed to ambient O2 in the test tube, are degraded on a scale of hours. Data on mitochondria show that the functional life span of a single liver mitochondrion, measured as the time between divisions, is as short as ten days-roughly equivalent to the turnover time of a rhodopsin membrane disk in a rod cell of the eye. We suggest that the human inner mitochondrial membrane is another example of such a specialized membrane based on its extraordinarily high percentage of polyunsaturated fatty acids, the presence of cardiolipin molecular species with four 18:2 chains, and its rapid turnover. We also propose that the relatively rapid rates of mitochondrial division evolved in part as a mechanism for rejuvenating the vast and oxidatively vulnerable inner membrane, thus avoiding effects from accumulation of oxidatively damaged cardiolipin and other phospholipids. Even though the energy cost of ssion is high, the benets are great and include the continuous production of virgin membrane surface, which avoids an oxidative chain reaction. The benets and risks of mitochondrial ssion are so powerful as to impact longevity.
