Growth dynamics of mitochondria in synchronized Chinese hamster cells.

The increase in cell volume (from electronic cell sizing) and the apportionment of this volume amongst the nuclear, cytoplasmic, and mitochondrial subcellular compartments (from electron microscopy) were studied throughout the cell division cycle in partially synchronized cultures of Chinese hamster V79-S171 cells. Average whole cell volume was found to increase smoothly, consistent with the doubling in one generation of individual cell volume. Nuclear size increased in like fashion. Mean total mitochondrial volume and number of mitochondria per cell both showed a different kind of variation, most notably a significant decrease in G(1) and G(2) as compared with mid S. These results are therefore counter to a model of simple doubling of mitochondria either synchronously with the cell division cycle or asynchronously. Absolute mean values per cell for log phase Chinese hamster cells were also determined, as follows: whole cell volume, 710 mu(3); nuclear volume, 190 mu(3); total mitochondrial volume, 37.5 mu(3); number of mitochondria per cell, 90.

Evidence of gene diminution during the formation of the macronucleus in the protozoan, Stylonychia (DNA density-melting curves-micronuclear DNA-polytene chromosomes).

The course of events by which a macronucleus is formed from a micronucleus after conjugation in the ciliated protozoan, Stylonychia, suggests that genetic diminution may occur. This idea is supported by determinations of the density profiles and melting curves for micro- and macronuclear DNAs. Macronuclear DNA consists of a single density component and melts as if it were a single component. Micronuclear DNA consists of four or more density components and melts as if it were a mixture of several DNAs of different base compositions. These data indicate that at least 60% of the micronuclear DNA components are absent from the macronuclear DNA.