Genetics, Mitosis

Introduction to Cell Division

Cell division is the process by which cells reproduce. In multicellular eukaryotes, mitotic cell division is primarily used for growth, repair, and replacement of cells, resulting in genetically identical daughter cells. The process involves DNA replication followed by mitosis and cytokinesis.

The Phases of Mitosis

Mitosis consists of five main phases: prophase (chromatin condenses, spindle forms), prometaphase (nuclear envelope breaks down, microtubules attach to kinetochores), metaphase (chromosomes align at the metaphase plate), anaphase (sister chromatids separate), and telophase (nuclei reform). Cytokinesis then divides the cytoplasm to form two daughter cells.

Cell Cycle Regulation

The cell cycle is strictly regulated by three main checkpoints: the G1/S checkpoint (restriction point), G2/M checkpoint (DNA replication verification), and the metaphase/anaphase checkpoint (spindle apparatus attachment). Failure of these checkpoints can lead to uncontrolled cell division and pathologies like cancer.

Cell Types and Proliferation

Cells are classified based on their division capacity: labile cells constantly proliferate (e.g., skin), quiescent/stable cells divide only when stimulated (e.g., hepatocytes), and permanent cells (e.g., cardiac muscle) are unable to proliferate.

Clinical Significance and Cancer

Cancer arises when cells bypass checkpoints and divide uncontrollably. Mutations in tumor suppressor genes, such as Rb and p53, are common drivers of tumorigenesis. Treatments often target these mechanisms; for instance, chemotherapy agents like Taxol stabilize microtubules to halt the cell cycle in rapidly dividing cancer cells.