The cell cycle is the process by which a cell grows, duplicates its DNA, and divides to produce two daughter cells. It consists of four main phases: G1, S, G2, and M.
Here’s a brief overview of each phase:
- G1 phase (First Gap phase): During this phase, the cell grows in size and prepares for DNA replication. It synthesizes proteins and other molecules, increases the number of organelles (such as mitochondria and ribosomes), and carries out its specialized functions. There is a checkpoint near the end of G1 (the G1/S checkpoint) to ensure the cell is ready to replicate its DNA.
- S phase (Synthesis phase): In this phase, the cell replicates its DNA. By the end of the S phase, each chromosome consists of two identical sister chromatids attached at a region called the centromere.
- G2 phase (Second Gap phase): The cell continues to grow and prepares for cell division. It synthesizes proteins necessary for mitosis and checks the quality of the replicated DNA. There is another checkpoint near the end of G2 (the G2/M checkpoint) to ensure the cell is ready to enter mitosis.
- M phase (Mitotic phase): The cell divides its genetic material and physical contents to create two daughter cells. Mitosis itself is divided into several stages (prophase, prometaphase, metaphase, anaphase, and telophase), followed by cytokinesis, the process by which the cytoplasm divides to form two separate cells.
In addition to these four main phases, cells can enter a quiescent state known as G0 when they are not preparing to divide. Cells can remain in G0 for varying amounts of time, and some cells (like nerve cells in adults) never leave this stage and are considered non-dividing, or “post-mitotic”.
The cell cycle is tightly regulated by a series of checkpoints and protein complexes that ensure the correct progression through the cycle. Any dysregulation in these processes can result in uncontrolled cell proliferation, a hallmark of cancer.
