Ageing of Cells

Telomeres are r etitive sequences at the ends of linear DNA molecules in eukaryotic chromosomes. With each round of replication in most normal cells, the telomeres are shortened because DNA polymerase cannot complete synthesis of the 5 end of each strand. This contributes to the aging of cells, because eventually the telomeres become so short that the chromosomes cannot function properly and the cells die. 

Koch and Schaechter (K3) have pointed out a number of unsatisfactory features in use of cell age as an index or measure of cell structure. In particular they note that the model based on this predicts no correlation between the life spans of sister cells, whereas in fact these life spans are found to be correlated. Again, they note that the mass of cells at division (bacterial cells, at any rate) shows less spread about a mean value than does the age of cells at division. They also report that they have found that the mean size of bacteria, at division, changes in a regular fashion when cells are transferred to a medium in which growth rate and bacterial size are different. 

Becerra, J., Andrades, J.A., Ertl, D.C., Sorgente, N., Nimni, M.E., 1996. Demineralized bone matrix mediates differentiation of bone marrow stromal cells in vitro effect of age of cell donor. J. Bone Miner Res. 11, 1703-1714. 

Unless special measures are taken, the distribution of local current over the surface of a fuel cell is nonuniform. Inhomogeneity in local current is detrimental for stable long-term operation of a cell. A large local current is accompanied by an increase in local polarization voltage and heating. These processes accelerate the ageing of cell components thereby reducing cell lifetime. 

The plot at the bottom of Fig. 2 gives an example also for the stochastic ageing of cells in a stack, as observed by the steady-state cell voltages. The scatter observed between cells at the EoL has considerably inaeased compared with that at the BoL. hi fact the standard deviation inaeased from 5mV per measured channel of two cells to 52mV. 

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