Levels of Enzyme Activity and Deoxyribonucleic Acid Synthesis in Mammalian Cells Cultured from the Animal

TL;DRAbstract

The replication of DNA in the cells of higher forms occurs only during part of the interphase of their division cycle (l-8).As a result, the cycles of plant and animal cells may be divided into four discrete phases: G1, the postmitotic period preceding DNA synthesis; S, the period of DNA synthesis; Gz, the premitotic period following DNA synthesis; and M, the relatively brief period of mitotic division (3).The very low rates of DNA synthesis and cell division characteristic of many tissues and organs of the adult mammal imply that control of cell multiplication involves blocks or restrictions in one or more of the phases of the division cycle.In fact, the diploid nature of most of these cells indicates that their control mechanisms are largely confined to the Gr, rather than to the Gs, period.This is consistent with the observation that the lengths of the S and Gz periods are relatively constant for most mammalian cells, whereas the G1 period generally governs the doubling time (9-l 1)

Chat with Paper

AI Agents for this Paper