What proteins are marked?

Surprisingly many of the proteins created in the cell are faulty from the start. They must be broken down and rebuilt since they can damage the organism. But perhaps the most important reason for a cell to get rid of a protein is that in this way the cell can control a given chemical reaction. By quickly destroying a protein that has a special function, the cell gets the same result as when one turns off a switch. When the proteins have been hacked to pieces, the cell can use their amino acids to synthesize other proteins. When protein degradation does not function correctly, we can become ill.