Animation of a molecular model of the 26S proteasome going through several conformations after being activated. The ribbon structure of the protein chain is shown in between. The 26S proteasome is a protein complex found in humans and other mammals. It is responsible for breaking up proteins that have been marked for degradation by ubiquitin tags. This role is critical in many cell systems including the cell cycle and gene expression. Disorders of the ubiquitin-proteasome system have been implicated in various diseases including Alzheimer's disease, Parkinson's disease, heart disease and cancer. This clip is available without labels, see K012/0255.