Cell age

The rate of product formation, rfi, depends upon the state of the cell population, environmental condition, temperature, pH, media composition and morphology with cell age distribution of the microorganism.2 3 A similar balance can be formulated for microbial biomass and cell concentration. The exponential phase of the microbial growth in a batch culture is defined by ... 

Wang, E. (1985). Are cross-bridging strucmres involved in the bundle formation of intermediate filaments and the decrease in locomotion that accompany cell aging J. Cell Biol. 100,1466-1473. 

Cell ageing and cell death. Edited by J. Davies and D.C. Sigee... 

All cell-wall extracts contained several PME isoforms differing in their isoelectric points. The isoenzyme patterns changed significantly during cell ageing. 

In the peel strong immunological depositions of acetyl esterase were found in epidermis, the small cells of the exocarp and in the oil cavities (Fig. 3 A,B,C). In the mesocarp and endocarp the immunological depositions were more moderate (Fig. 3 D), but strong immunological depositions were found in the vascular bundles, especially in xylem. The immunological depositions in the peel seem to be correlated with cell size or cell age. The small cytoplasma rich cells have a higher content of acetyl esterase. 

The ability of bacteria to accumulate toxic metals also varies with cell age. Shuttleworth and Unz (1993) reported that one-day-old cells of Thiothrix strain Al accumulated considerably less Ni or Zn than its 2-5 day old... 

In many processes, cells may die continuously or may start dying (after time, t3) because of a lack of nutrients, toxic effects or cell ageing. This process can typically be described by a first order decay relationship ... 

The fact that receptors need to be replaced via de novo biosynthesis can be demonstrated in experiments where neutrophils are cultured in the presence and absence of cycloheximide. When protein biosynthesis is blocked by this inhibitor, the expression of FcyRIII on the cell surface cannot be maintained as the cells age in culture (Fig. 7.8), indicating that continued expression of this receptor is a balance between the amount shed and the amount replaced via new biosynthesis. Newly synthesised receptors appear to be functional, because they can be detected within the biosynthetic machinery of the cell, and newly made (i.e. newly labelled) receptors are detected in the plasma membrane. 

Davies, I. Sigee, D. C. Cell Ageing and Cell Death Soc. Exp. Biol. Sem. Ser. 25 Cambridge University Cambridge, 1984. 

Davis, T., Baird, D. M., Haughton, M. F., Jones, C. J., and Kipling, D. (2005). Prevention of accelerated cell aging in Werner syndrome using a p38 mitogen-activated protein kinase inhibitor. J. Gerontol. A Biol. Sci. Med. Sci. 60,1386-1393. 

Although the activity of the normal enzyme declines as red cells age, even the oldest cells have a sufficient level of activity to provide protection against... 

Decline of erythrocyte G6PD activity with cell age for the three most commonly ecountered forms of the enzyme. 

If ris the cell age then the instantaneous rate of product formation under constant environmental conditions is assumed to take the form ... 

As a whole, PolyPs in cells of eukaryotes are characterized by plural localization, depending on the cell age or environmental conditions. For example, cytochemical data on the localization of PolyPs in the cells of Saccharomyces cerevisiae are presented in Figure 5.2, according to Vofisek et al. (1982). Further studies of this problem may provide new data on the functions of these biopolymers. 

Fig. 12.12 With each cell division, the telomeies at the end of the chromosomes become shortened. The model shows that in order to stop senescence and death, both telomerase activity and blockage of the RB pathway are needed. Telomerase activity and blockage of the RB pathway are intimately linked, because the factors that block the RB pathway (the wyc oncogene and the E6 oncogene of the human papillomavirus, see Part 4) also upr late expression of hTERT.24 In contrast to normal differenbated cells, cancer cells have telomerase adivity. In this way, cancer cells overturn the life-sparvcontrolling clock and become immortal. Since, about 90% of all human cancers are derived from epithelial cells, it follows that in epithelial cancer cells the RB pathway has also been inactivated. To the contrary, when the tumour-suppressor p 53 accumulates, the cells age prematurely.25...

Subsequently, a protein component of telomerases also was identified. From its amino acid sequence, this component is clearly related to reverse transcriptases, enzymes first discovered in retroviruses that copy RNA into DNA. Thus, telomerase is a specialized reverse transcriptase that carries its own template. Telomeres may play important roles in cancer-cell biology and in cell aging. 

HK deficiency (OMIM 235700) is a rare, recessively inherited disease with chronic nonspherocytic hemolytic anemia as the predominant clinical feature. The phenotypic expression of the disease is heterogeneous, as with most glycolytic red cell enzyme deficiencies. The spectrum ranges between severe neonatal hemolysis and death to a fully compensated chronic hemolytic anemia. Patients benefit in general from a splenectomy. Red cell morphology is normal. Since HK activity is dependent on red cell age, reticulocytosis, always present in HK-deficient patients, may obscure enzyme deficiency. Other age-dependent red cell enzymes (e.g., pyruvate kinase and/or G6PD) should be measured simultaneously as an internal control to assess the influence of reticulocyte enzyme activity. 

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