Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 11.5 Apoptosis Requires Integration of Multiple Cell-Signaling Pathways
Apoptosis, or programmed cell death, is a controlled cellular process triggered by signals from outside or inside the cell. It plays essential roles in development, immunity, and the elimination of damaged cells.
What Is Apoptosis?
- A type of programmed cell death
- Involves DNA fragmentation, organelle breakdown, and packaging of cell parts into vesicles
- Prevents inflammation or damage to neighboring cells
- Triggered by signals that activate a cascade of molecular events inside the cell
Molecular Mechanisms
- Studied in Caenorhabditis elegans (C. elegans), a model organism
- Key genes: ced-3, ced-4, and ced-9
- Ced-9 inhibits apoptosis by blocking Ced-4 and Ced-3
- A death signal inactivates Ced-9, releasing Ced-4 to activate Ced-3, a caspase protease
- Caspases break down cellular components, leading to cell death
Apoptosis in Mammals
- Multiple signaling pathways (involving ~15 caspases) control apoptosis
- One major pathway: Mitochondria release proteins (e.g., cytochrome c) that promote apoptosis
- Other pathways involve external death signals binding to cell-surface receptors
- Internal signals include DNA damage or ER stress from misfolded proteins
Importance and Applications
- Essential for nervous system and immune system development
- Shapes body structures during embryonic development (e.g., removal of tissue between fingers)
- Failure of apoptosis: can lead to cancer (e.g., melanoma)
- Excessive apoptosis: linked to neurodegenerative diseases (e.g., Alzheimer’s, Parkinson’s)
- Apoptosis is evolutionarily conserved across animals, fungi, and even some unicellular eukaryotes
In a Nutshell
Apoptosis is a vital, tightly regulated process in which signals trigger a cascade that dismantles a cell. It eliminates unneeded or damaged cells and integrates multiple signaling pathways to make life-or-death decisions.