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.