Apoptosis
Apoptosis is a form of programmed, genetically regulated cell death that occurs in multicellular organisms as a normal and controlled part of development and homeostasis. It is characterised by cell shrinkage, chromatin condensation, membrane blebbing, and fragmentation into apoptotic bodies that are cleared by phagocytes without triggering inflammation. Dysregulation of apoptosis is implicated in cancer (insufficient apoptosis) and neurodegenerative diseases (excessive apoptosis).
Comparison of Apoptosis and Necrosis
| Feature | Apoptosis | Necrosis |
|---|---|---|
| Trigger | Programmed / physiological signals | Uncontrolled injury or toxins |
| Cell morphology | Shrinkage, blebbing | Swelling, lysis |
| Inflammation | None (anti-inflammatory) | Significant inflammatory response |
| DNA fragmentation | Internucleosomal (laddering pattern) | Random, smear pattern |
| Energy requirement | ATP-dependent | Passive, no ATP needed |
| Outcome | Apoptotic bodies phagocytosed | Cellular debris, tissue damage |
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Related Terms
Cell Cycle
The cell cycle is the ordered sequence of events by which a cell grows, replicates its DNA, and divides into two daughter cells. It consists of interphase (G1, S, and G2 phases) and the mitotic phase (mitosis and cytokinesis). Precise regulation of the cell cycle through checkpoints is essential for normal development; dysregulation leads to cancer and other diseases.
Stem Cell
A stem cell is an undifferentiated cell capable of self-renewal and differentiation into specialised cell types. Stem cells are found in embryos (embryonic stem cells) and adult tissues (adult stem cells), serving as a repair and replenishment system throughout life. Their unique plasticity makes them central to regenerative medicine, disease modelling, and therapeutic research.
Cell Signaling
Cell signaling refers to the complex system of communication by which cells detect, process, and respond to chemical signals from their environment or neighbouring cells. Signaling pathways typically involve a ligand binding to a receptor, triggering an intracellular cascade of molecular events that alter gene expression, metabolism, or cell behaviour. It governs fundamental processes such as growth, differentiation, immune responses, and apoptosis.
From Greek "apo" (away from) + "ptosis" (falling). The term was introduced by John Kerr, Andrew Wyllie, and Alastair Currie in 1972 to describe the falling away of leaves from a tree as a metaphor for cellular self-elimination.