Recycling the cell's power plants
Mitochondria wear out, and a cell that kept damaged ones would accumulate leaky organelles that waste fuel and spill reactive oxygen species. Mitophagy is the housekeeping process that recognizes failing mitochondria and routes them for breakdown and reuse of their parts.
Depolarization, a drop in the inner membrane voltage, is the common trigger. The kinase PINK1 stabilizes on the surface of such a mitochondrion and brings in Parkin, which coats outer membrane proteins with ubiquitin to mark the organelle as cargo.
Why turnover matters for tissue health
Tagged mitochondria are wrapped by an autophagosome and delivered to lysosomes, where their components are degraded into amino acids, lipids, and nucleotides that the cell can recycle. Balanced mitophagy alongside the biogenesis of new mitochondria keeps the population healthy.
Exercise and fasting are studied as states that influence mitochondrial turnover, but the human evidence is still developing and effects vary by tissue and individual. This is general educational information about a cellular process, not health or lifestyle advice; consult a qualified professional for personal guidance.