cell cycle phase transition

Definition

Target type: biologicalprocess

The cell cycle process by which a cell commits to entering the next cell cycle phase. [GOC:mtg_cell_cycle]

Cell cycle phase transitions are precisely regulated events that ensure the accurate duplication and segregation of the genome, maintaining genetic stability. These transitions are driven by a complex interplay of cyclin-dependent kinases (CDKs), their regulatory subunits cyclins, and other regulatory proteins.

The cell cycle is typically divided into four phases: G1, S, G2, and M.

**G1 Phase:** The first gap phase is characterized by cell growth and preparation for DNA replication. CDK4/6 complexes, activated by cyclins D1, D2, and D3, phosphorylate the retinoblastoma protein (Rb), leading to its inactivation. This allows for the transcription of genes required for S phase entry.

**S Phase:** During this phase, DNA replication occurs. CDK2, activated by cyclin A, promotes the activation of DNA replication machinery.

**G2 Phase:** The second gap phase involves further cell growth and preparation for mitosis. CDK1, activated by cyclin B, is crucial for the transition from G2 to M phase.

**M Phase:** This phase encompasses both mitosis (nuclear division) and cytokinesis (cytoplasmic division). CDK1-cyclin B complex triggers the breakdown of the nuclear envelope, chromosome condensation, spindle formation, and ultimately, the separation of sister chromatids.

**Regulation of Transitions:**

* **Cyclin-CDK Complexes:** The activity of CDKs is tightly regulated by cyclins, which bind to CDKs to activate them. The levels of cyclins fluctuate during the cell cycle, ensuring that CDKs are active only at specific phases.
* **CDK Inhibitors:** These proteins, such as p21 and p27, bind to and inhibit CDKs, preventing premature entry into the next phase.
* **Checkpoints:** The cell cycle includes checkpoints that monitor critical events, such as DNA replication and chromosome attachment to the spindle. These checkpoints can arrest the cycle if problems are detected, preventing errors in cell division.
* **External Signals:** Growth factors and other extracellular signals can influence cell cycle progression, ensuring that cells divide only when appropriate.

**Errors in Phase Transition:** Dysregulation of the cell cycle can lead to uncontrolled cell proliferation, a hallmark of cancer. Mutations in genes encoding CDKs, cyclins, CDK inhibitors, or checkpoint proteins can contribute to uncontrolled cell division.'
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Proteins (2)

Compounds (132)