Proteasome
<p><b>Proteasomes </b>are protein complexes inside all eukaryotes and archaea, and in some bacteria. The main function of the proteasome is to degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds.   In eukaryotes, proteasomes are located in the nucleus and the cytoplasm.
 
In structure, the <b>proteasome </b>is a cylindrical complex containing a "core" of four stacked rings forming a central pore. Each ring is composed of seven individual proteins. The inner two rings are made of seven β subunits that contain three to seven protease active sites. 
 
<img src="/a431211d-be03-5793-b13a-c5df06a29c9a.png"/>  <img src="/119d3005-dabe-5bc2-b06f-76199028036d.png"/>   <img src="/67902f86-675f-5811-aaaa-f36931983928.png"/>
 
   The <b>Ubiquitin Proteasome Pathway (UPP)</b> is the principal mechanism for protein catabolism in the mammalian cytosol and nucleus. The highly regulated UPP affects a wide variety of cellular processes and substrates and defects in the system can result in the pathogenesis of several important human diseases. The central role of the UPP in biology has been recognized with the Nobel Prize for Chemistry which was awarded to Avram Hershko, Aaron Ciechanover and Irwin Rose in 2004.</p>