4.6 Regulation of Cell Cycle
- Syllabus
- 2025
- Topic
- 4.6
- Level
- —
Learning objectives
4.6A—Describe the role of checkpoints in regulating the cell cycleDescribe the role of checkpoints in regulating the cell cycle.• A number of internal controls or checkpoints regulate progression through the cell cycle.• Interactions between cyclins and cyclindependent kinases control the cell cycle.- Exclusion: Knowledge of specific cyclin-CdK pairs or growth factors is beyond the scope of the AP Exam.4.6B—Describe the effects of disruptions to the cell cycle on the cell or organismDescribe the effects of disruptions to the cell cycle on the cell or organism.• Disruptions to the cell cycle may result in cancer or apoptosis (programmed cell death).
Checkpoints Control Progress Through the Cell Cycle
Cell-cycle checkpoints are internal control points that determine whether a cell proceeds to the next stage, pauses while a problem is corrected, or stops dividing. They prevent later events from beginning before critical earlier events are complete.
A checkpoint can respond to conditions such as damaged or incompletely replicated DNA and chromosomes that are not correctly attached for separation. If requirements are met, progression continues; if not, the cycle is delayed or halted.
Cyclins interact with cyclin-dependent kinases (CDKs) to regulate this progression. Changes in the availability or activity of these regulators change whether cell-cycle targets are activated, linking checkpoint information to a go-or-stop outcome.
For the AP Exam, understand the control principle and consequences. Memorizing specific cyclin-CDK pairs or particular growth factors is outside the required scope.
When Cell-Cycle Control Is Disrupted
Disrupting cell-cycle control changes whether a cell with damage divides, stops, or dies. The outcome depends on which control signal is altered and whether checkpoint and apoptosis pathways still function.
| Control change | Cellular effect | Possible organism-level result |
|---|---|---|
| A checkpoint, contact-inhibition signal, or growth-control pathway loses restraint | A cell proceeds through the cycle when it should pause or stop | Repeated uncontrolled division can contribute to a tumor and cancer |
| Severe damage activates programmed cell death | The damaged cell is dismantled instead of continuing to divide | Apoptosis prevents that cell from passing damaged DNA to daughter cells |
| A mutation disables both arrest and apoptosis responses | Damage persists while the cell continues dividing | Additional abnormalities can accumulate, increasing cancer risk |
Predict effects in causal order: identify the disrupted regulator or checkpoint → decide whether progression, arrest, or apoptosis changes → state how division and inheritance of damaged DNA change → connect that cellular outcome to cancer risk when justified.
Apoptosis is not uncontrolled cell division. It is a regulated cell-death response; cancer is associated with cells continuing to divide despite controls that should restrain them.