Final answer:
Cyclins are classified into four classes that regulate the progress of vertebrate somatic cells and yeast cells through the cell cycle. Cyclins and Cdks work together at various checkpoints to ensure each phase is completed properly before moving on to the next, with fluctuations in cyclin levels as a regulatory mechanism. More complex eukaryotes utilize additional cyclin/Cdk pairings for further cell cycle control.
Step-by-step explanation:
Cyclins can be categorized into four classes based on their behavior during the cell cycle in vertebrate somatic cells and in yeast cells. These classes are associated with different checkpoints and phases of the cell cycle. Cyclins and cyclin-dependent kinases (Cdks) work in tandem to control the progress through these phases, ensuring that each stage of the cell cycle, from interphase to mitosis, is completed correctly before moving on to the next. Cyclins accumulate at various points during the cell cycle in response to internal and external signals and then are degraded after the cell moves to the next stage. This fluctuation helps regulate the cell cycle along with other substances such as growth factors, tumor suppressor proteins, and additional regulatory molecules.
Dividing yeast cells utilize three of these checkpoints whereas more complex eukaryotes use additional cyclin/Cdk pairings to control the cell cycle at various junctures. The general processes involve the cell growing during interphase (subdivided into G1, S, and G2 phases) and then dividing during the mitotic phase. The control molecules like cyclins and Cdks play critical roles in making sure the cell cycle progresses smoothly through its intricately timed events.