Aging Aging

Mitochondrial DNA Mutations 24519Analysis of Mitochondrial DNA MutationsDeletionsRobert W. Taylor, Theresa M. Wardell, Emma L. Blakely,Gillian M. Borthwick, Elizabeth J. Brierley,and Douglass M. Turnbull1. IntroductionAlthough the precise mechanisms of the aging process remain poorly understood,a plausible theory for cellular dysfunction and deterioration during aginginvolves mitochondria (1,2). The major function of mitochondria is to generateenergy for cellular processes in the form of ATP by oxidative phosphorylation.Mitochondria contain their own DNA (mtDNA), a small 16.5 kb circular moleculethat encodes 13 essential polypeptides of the mitochondrial respiratorychain, as well as 2 rRNAs and 22 tRNAs required for intramitochondrial proteinsynthesis (3). The mitochondrial respiratory chain is a series of five,multisubunit protein complexes located within the inner mitochondrial membrane.The first four of these (complexes I–IV) reoxidize reduced cofactors(NADH and FADH 2 ) generated by the oxidation of foodstuffs, thereby generatingan electrochemical gradient across the inner mitochondrial membranewhich is harnessed by the fifth complex, the ATP synthetase, to drive the formationof ATP.The mitochondrial aging hypothesis proposes that aging results from theaccumulation of detrimental mtDNA mutations during life, compromising thecellular production of ATP to such a degree that it results in cellular dysfunctionand death. A number of features help to explain why mtDNA is particularlyvulnerable to deleterious mutational events. The mitochondrial genomehas a mutation rate some 10-fold greater than that of nuclear DNA, lacks protectivehistones, and possesses few and inefficient DNA repair mechanisms. ItFrom: Methods in Molecular Medicine, Vol. 38: Aging Methods and ProtocolsEdited by: Y. A. Barnett and C. R. Barnett © Humana Press Inc., Totowa, NJ245