title: A bimolecular mechanism for the cell size control of the cell cycle.
abstract: A molecular model for the control of cell size has been developed. It is based on two molecules, one (I) acts as an inhibitor of the entrance into S phase, and it is synthetised just after cell separation in a fixed amount per nucleus. The other (A) is an activator of the S phase, and it is synthetised at a ratio proportional to the overall protein accumulation. The activator reacts stoichiometrically with (I), and after all the (I) molecules have been titrated, (A) begins to accumulate. When it reaches a threshold value, it triggers the onset of DNA replication. This model was tested by simulation and when applied to the case of unequal division explains a number of features of an exponentially growing yeast cell population: (a) the lengths of TP (cycle time of parent cells) and TD (cycle time of daughter cells) verify the condition exp(- KTP ) + exp(- KTD ) = 1; (b) the changes of the average cell size of populations at different growth rates; (c) the frequency of parents and daughters at various growth rates; (d) the increase of cell size at bud initiation for cells of increasing genealogical age; (e) the existence of a TP - TB period (difference between the cycle time of parents and the length of budded phase) that depends linearly upon the doubling time of the population.
mesh_terms: D002453:Cell Cycle; D004261:DNA Replication; D005656:Fungal Proteins / Q000378:metabolism; D007399:Interphase; D008954:Models, Biological; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism; D012568:Schizosaccharomyces / Q000166:cytology / Q000378:metabolism; D013997:Time Factors
chemical_list: D005656:Fungal Proteins