A large protein complex that degrades proteins tagged with ubiquitin, functioning as the cell's primary protein recycling system. The 26S proteasome recognizes ubiquitin-tagged proteins and breaks them down into small peptides.
The name combines 'protein' and 'lysosome' (from Greek 'lysis' meaning to break down), coined in the 1980s when scientists realized cells had a sophisticated protein degradation machine distinct from lysosomes. The structure resembles a molecular barrel with caps.
The proteasome is like a molecular paper shredder that only accepts documents with the right security clearance (ubiquitin tags)! It's so precise that it can degrade one specific protein while leaving identical copies untouched if they lack the degradation signal.
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