Final answer:
The statement that cyclins are proteins associated with the regulation of cell growth is true. Cyclins operate in conjunction with cyclin-dependent kinases to control the cell cycle by forming complexes that get phosphorylated to become active, and their concentrations fluctuate to regulate the cell cycle progression.
Step-by-step explanation:
Cyclins are proteins that are indeed associated with the regulation of cell growth, making the statement true. These proteins, along with cyclin-dependent kinases (Cdks), act as positive regulators and are essential for the cell to progress through various checkpoints during the cell cycle. The levels of cyclins rise and fall in a predictable pattern throughout the cycle. When cyclins bind to Cdks, they form a complex that must be phosphorylated to be fully active. The phosphorylation of the Cdk/cyclin complex changes the shape of the proteins involved, activating them to push the cell into the next phase. After a cell progresses to a new phase, the active cyclins from the previous phase get degraded by cytoplasmic enzymes. Thus, the concentration of cyclins at different points in the cycle determines when and which Cdk/cyclin complexes form, ensuring precise regulation and timing of cell cycle events.