Final Answer:
In the budding yeast, *Saccharomyces cerevisiae*, START is a step in the progression through G1 in which the cell commits to proceeding into S-phase and undergoing one round of cell division.
Step-by-step explanation:
In the cell cycle of budding yeast, *Saccharomyces cerevisiae*, the START checkpoint is a crucial point in the G1 (Gap 1) phase. At START, the cell makes a critical decision to commit to the cell cycle progression, signaling the entry into the S-phase where DNA synthesis occurs. The decision to initiate the cell cycle is tightly regulated, and it involves the activation of cyclin-dependent kinases (CDKs) and their binding to specific cyclins.
The G1 phase is a period of cell growth and preparation for DNA replication. Before the cell can progress to the S-phase, it must pass the START checkpoint. Cyclin-dependent kinases (CDKs) play a central role in regulating the cell cycle, and their activity is controlled by the availability of specific cyclins. In budding yeast, the G1 cyclins, along with the CDKs, regulate the passage through START. Once the cell passes this checkpoint, it commits to completing the cell cycle, including DNA synthesis and cell division.
Understanding the regulation of the cell cycle, particularly the events at the START checkpoint, is essential in unraveling the mechanisms that control cell growth and division. The precise coordination of molecular events at START ensures that cells progress through the cell cycle in a controlled and orderly manner, contributing to the overall integrity and health of the organism.