The cell cycle is controlled in most cells by

The cell cycle is primarily controlled by a family of proteins called cyclins and cyclin-dependent kinases (CDKs). These proteins regulate the progression of the cell cycle by coordinating the transitions between different phases, ensuring that cell division occurs in a timely and orderly manner.

The activity of cyclin-CDK complexes fluctuates throughout the cell cycle, with different cyclins being expressed and degraded at specific points in the cycle. Cyclins bind to and activate specific CDKs, leading to the phosphorylation of target proteins that drive cell cycle progression.

The activity of cyclin-CDK complexes is tightly regulated by various mechanisms, including:

1. Transcriptional Regulation: The expression levels of cyclins and CDKs are regulated transcriptionally, ensuring that they are produced at the appropriate times in the cell cycle.

2. Post-translational Modifications: Cyclins and CDKs undergo post-translational modifications, such as phosphorylation and ubiquitination, which can affect their stability, activity, and subcellular localization.

3. Inhibitory Proteins: Cyclin-CDK activity is also regulated by inhibitory proteins, such as CDK inhibitors (CKIs), which bind to and inhibit cyclin-CDK complexes, preventing them from phosphorylating their target proteins.

4. Checkpoint Controls: Checkpoint mechanisms monitor the integrity of the genome and ensure that cell cycle progression proceeds only if conditions are favorable. Checkpoint proteins detect DNA damage or replication errors and can halt the cell cycle at specific checkpoints until the issues are resolved.

Overall, the coordinated activity of cyclins and CDKs, along with the regulation by various other proteins and checkpoint controls, ensures that the cell cycle proceeds accurately and efficiently, maintaining genomic stability and preventing aberrant cell division.