Well, let's suppose it was damaged. How exactly does the cell know to break down that particular protein that was damaged and leave all the other normal proteins untouched? Well, the answer lies in a 76 amino acid population polypeptide known as Ubiquitin. So Ubiquitin is this marker for those proteins that needs to be broken down. And before the protein is actually broken down, it undergoes a process known as Ubiquit nation. That is, we attach many Ubiquitant molecules onto that target protein that needs to be broken down.