Final answer:
The regulation of the START phase in Saccharomyces cerevisiae is linked to the integration of environmental cues such as nutrient availability, presence of mating factors, and cell size. Saccharomyces cerevisiae can undergo sexual reproduction by secreting mating factors that signal readiness to mate to other haploid cells. This species can also reproduce asexually by budding.
Step-by-step explanation:
The student's question refers to the regulation of the START phase of the cell cycle in the budding yeast, Saccharomyces cerevisiae. This yeast species uses a complex signaling network to integrate a variety of environmental cues before committing to a new round of cell division. The availability of nutrients, the presence of mating factors, and achieving a certain cell size, are among the critical signals that are processed. When conditions are favorable, including sufficient nutrients and the presence or absence of mating factors, Saccharomyces cerevisiae can undergo sexual reproduction by the release of a signaling molecule called mating factor. This ligand molecule communicates to nearby haploid yeast cells of the opposite mating type their readiness to mate, after which two haploid cells can fuse to form a diploid cell.
During the process of sexual reproduction, the mating factor binds to cell-surface receptors, causing the receiving cell to pause its normal growth and initiate a signaling cascade using protein kinases and GTP-binding proteins akin to G-proteins. In addition to sexual reproduction, budding yeast, like Saccharomyces cerevisiae, can also reproduce asexually through a process called 'budding', which allows a daughter cell to form from an outgrowth of the parent cell. Both haploid and diploid states are seen in Saccharomyces cerevisiae cultures, which can be maintained under specific culture conditions.