Cell Cycle and Division
The cell cycle is the ordered sequence of events by which a cell duplicates its contents and divides into two daughter cells. This area gathers the essentials of how cells progress through interphase and division, how that progression is regulated and policed, and how the two principal forms of nuclear division — mitosis and meiosis — produce somatic and germ cells respectively.
Definition
The cell cycle is the recurring series of phases — interphase (G1, S, G2) followed by the mitotic phase (M) — through which a eukaryotic cell grows, replicates its DNA, and partitions its genome and cytoplasm into two daughter cells, governed by oscillating cyclin-dependent kinase activity and surveillance checkpoints.
Scope
The area covers the four phases of the eukaryotic cell cycle (G1, S, G2, M), the cyclin and cyclin-dependent kinase machinery that drives progression, the surveillance checkpoints that maintain genomic integrity, the mechanics of mitosis and cytokinesis, the reductional and equational divisions of meiosis, and programmed cell death as a complementary control on cell number. It treats these as structural and regulatory cell-biology topics rather than as clinical guidance.
Sub-topics
Key concepts
- Interphase (G1, S, G2) and M phase
- Cyclins and cyclin-dependent kinases (CDKs)
- DNA replication and chromosome segregation
- Cell cycle checkpoints
- Restriction point and commitment to division
- Mitosis versus meiosis
- Programmed cell death (apoptosis)
Mechanisms
Progression through the cycle is driven by the periodic activation of cyclin-dependent kinases, whose activity rises and falls as their regulatory cyclin partners are synthesised and then destroyed. Nurse and colleagues showed that a single CDK (Cdc2/CDK1) acts as a universal trigger for entry into mitosis across eukaryotes, while Morgan's synthesis frames CDKs as the engines and clocks of the cycle. Hartwell and Weinert defined checkpoints as control circuits that halt the cycle until prior steps — such as complete DNA replication or correct chromosome attachment — are finished, ensuring that events occur in the right order. Cancer biology, reviewed by Vermeulen and colleagues, illustrates how deregulation of these controls underlies uncontrolled proliferation.
Clinical relevance
Understanding the cell cycle underpins how proliferation, tissue renewal, and aneuploidy are described in the health sciences, and how many anticancer agents are conceptualised as acting on dividing cells. This area describes normal and deregulated cell division at a reference level and is not a basis for diagnostic or treatment decisions.
History
Modern understanding of the cell cycle emerged in the late twentieth century from genetics of yeast and biochemistry of marine invertebrate eggs: Nurse's work on fission yeast identified the universal mitotic kinase, the discovery of cyclins explained its periodic activation, and Hartwell and Weinert's checkpoint concept explained how order and fidelity are enforced. The 2001 Nobel Prize in Physiology or Medicine recognised Hartwell, Hunt, and Nurse for these discoveries.
Key figures
- Leland Hartwell
- Paul Nurse
- Timothy Hunt
- David Morgan
Related topics
Seminal works
- hartwell-weinert-1989
- nurse-1990
- morgan-1997
Frequently asked questions
- What are the phases of the cell cycle?
- Interphase comprises G1 (growth), S (DNA synthesis), and G2 (growth and preparation), and is followed by M phase, in which the nucleus divides by mitosis and the cell divides by cytokinesis; non-dividing cells may rest in a quiescent state called G0.
- How is the cell cycle different from cell division?
- The cell cycle is the whole repeating sequence a cell passes through between divisions, whereas cell division (mitosis with cytokinesis, or meiosis) is the M-phase portion in which one cell becomes two or, in meiosis, four.