cyclin

Examples of cyclin in the following topics:

• Regulator Molecules of the Cell Cycle

  • Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are responsible for the progress of the cell through the various checkpoints.
  • Cyclins regulate the cell cycle only when they are tightly bound to Cdks.
  • The levels of Cdk proteins are relatively stable throughout the cell cycle; however, the concentrations of cyclin fluctuate and determine when Cdk/cyclin complexes form.
  • The concentrations of cyclin proteins change throughout the cell cycle.
  • Also, note the sharp decline of cyclin levels following each checkpoint (the transition between phases of the cell cycle) as cyclin is degraded by cytoplasmic enzymes.

• Regulation of the Cell Cycle at Internal Checkpoints

  • This transition, as with all of the major checkpoint transitions in the cell cycle, is signaled by cyclins and cyclin dependent kinases (CDKs).
  • Cyclins are cell-signaling molecules that regulate the cell cycle.
  • If the DNA has been correctly replicated, cyclin dependent kinases (CDKs) signal the beginning of mitotic cell division.

• Proto-oncogenes

  • For example, a mutation that allows the Cdk gene to be activated without being partnered with cyclin could push the cell cycle past a checkpoint before all of the required conditions are met.