Changes in the Incorporation of Carbon Derived from Glucose into Cellular Pools During the Cell Cycle of Saccharomyces Cerevisiae

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Abstract
The rate of incorporation of 14C derived from [U-14C]glucose into cells of Saccharomyces cerevisiae X2180(1B) was investigated as a function of the cell cycle. After pulse-labelling of exponentially growing populations, centrifugal elutriation was used to isolate various cell fractions of increasing cell size, representing successive stages of the cell cycle. The total amount of 14C incorporated per cell was found to increase continuously during the cell cycle along with cellular protein content and Coulter counter cell volume. This pattern supports the model of exponential cell growth. In order to evaluate changes in intracellular carbon flow during the cell cycle, chemical extraction procedures were used to obtain four cellular fractions enriched in either low-molecular-mass components, lipid material, polysaccharides or proteins. The distribution of 14Camong these cellular fractions varied during successive stages of the cell cycle, indicating cell-cycle-dependent fluctuations in intracellular carbon flow. During the G1 phase the flow of 14C into the low-molecular-mass pool increased markedly; concurrently, the rate of incorporation into the polysaccharide-enriched pool decreased.