Cell Cycle and Division
The cell cycle is the ordered sequence by which a cell duplicates its contents and divides into two daughter cells, governed by a control system that enforces correct timing and order.
Definition
The cell cycle is the repeating series of events, comprising DNA replication and division, by which one cell becomes two; cell division is the physical partitioning of a cell's contents into daughter cells.
Scope
This area covers the phases of the cell cycle, the molecular control system of cyclins and cyclin-dependent kinases and its checkpoints, the mechanics of mitosis and cytokinesis that distribute duplicated chromosomes, and meiosis, the specialized division that produces gametes.
Sub-topics
Core questions
- What are the phases of the cell cycle and what happens in each?
- How do cyclins and cyclin-dependent kinases drive cell-cycle progression?
- How do checkpoints ensure events occur in the correct order?
- How do mitosis and meiosis differ in their outcomes?
Key theories
- Cyclin–CDK control of the cell cycle
- Cell-cycle progression is driven by cyclin-dependent kinases whose activity rises and falls with the synthesis and destruction of cyclin partners, triggering each phase transition in order.
- Genetic control of the cell division cycle
- Mutations in defined genes block the cell cycle at specific points, showing that division is governed by an ordered genetic program rather than a passive series of reactions.
Mechanisms
The cell cycle proceeds through G1, S phase where DNA is replicated, G2, and M phase where the cell divides. A control system based on cyclin-dependent kinases, activated by cyclins and modulated by phosphorylation and inhibitors, triggers transitions. Checkpoints monitor cell size, DNA integrity, replication completion, and chromosome attachment, halting progression until conditions are met. In M phase the mitotic spindle segregates chromosomes and cytokinesis splits the cytoplasm; meiosis adds a recombination step and a second division to halve the chromosome number.
Clinical relevance
The cell cycle underlies growth, tissue renewal, and reproduction, and its control system is a cornerstone of cell and developmental biology. The treatment here is descriptive and non-prescriptive.
History
Hartwell's yeast genetics defined cell-division-cycle genes and checkpoints; Nurse identified the key cyclin-dependent kinase, and Hunt discovered cyclins as periodically destroyed regulators, together establishing the molecular control of the cell cycle.
Key figures
- Leland Hartwell
- Paul Nurse
- Tim Hunt
- David Morgan
Related topics
Seminal works
- evans1983
- hartwell1974
Frequently asked questions
- What are cyclin-dependent kinases?
- They are enzymes that drive the cell cycle forward by phosphorylating target proteins, but only when bound to a cyclin partner, so their activity is timed by the rise and fall of cyclins.
- What is the purpose of cell-cycle checkpoints?
- Checkpoints pause the cycle until key conditions are met, such as completed and undamaged DNA replication and proper chromosome attachment, ensuring that division produces correct daughter cells.