The cell cycle is a fundamental biological process describing the organized series of events a cell undergoes as it prepares for and completes division. This cycle is essential for growth, development, and repair in living organisms, enabling the increase of cell populations, replacement of damaged cells, and the formation of multicellular organisms.
Interphase: The Cell’s Preparatory Stages
Interphase is the longest phase of the cell cycle, during which the cell grows and prepares for division. This preparatory period is subdivided into three distinct stages: G1, S, and G2.
The G1 phase, or “first gap,” marks a period of significant cellular growth and metabolic activity. The cell increases in size and synthesizes proteins and organelles needed for its functions and division. It also assesses its environment to determine if conditions are suitable for division. Cells not receiving signals to divide may enter a quiescent G0 phase, remaining metabolically active but not preparing for division.
Following G1, the cell enters the S phase, or “synthesis phase,” characterized by DNA replication. The cell’s entire genome is copied, resulting in two identical sets of chromosomes. Each chromosome consists of two sister chromatids, which remain joined. This duplication ensures each daughter cell receives a complete and identical set of genetic material.
The G2 phase, or “second gap,” serves as a final preparatory stage before division. The cell continues to grow, synthesizes proteins needed for mitosis, and replenishes energy stores. This phase includes checkpoints to verify accurate DNA replication and absence of genetic errors. Successful completion of G2 signifies the cell is ready to proceed into the mitotic phase.
Mitotic Phase: The Division Process
The mitotic (M) phase is the culmination of the cell cycle, where the prepared cell physically divides into two daughter cells. This phase is composed of two primary, sequential events: mitosis and cytokinesis. The M phase is a relatively short period compared to interphase, often lasting less than an hour.
Mitosis is the process of nuclear division, during which duplicated chromosomes are separated into two new nuclei. This process is divided into several stages: prophase, metaphase, anaphase, and telophase. Throughout these stages, condensed chromosomes are organized and pulled apart by the mitotic spindle, ensuring each new nucleus receives an identical set of genetic information.
Following nuclear division, cytokinesis completes the M phase by dividing the cell’s cytoplasm and organelles. This separation typically begins during the late stages of mitosis, overlapping with anaphase or telophase. In animal cells, a contractile ring of actin filaments forms, pinching the cell in two to create a cleavage furrow. Plant cells form a cell plate from vesicles that grows outwards, eventually forming a new cell wall to separate the daughter cells. Mitosis and cytokinesis result in two genetically identical daughter cells.