Proteolysis is the process in which proteins are destroyed in eukaryotic cells. Lysosome plays an important role in protein degradation. During starvation, the long lived proteins are being destroyed for the source of energy.
If the protein degradation is not aided by lysosome then there is another pathway for degradation of proteins in eukaryotes and is Ubiquitin based degradation. Protein degradation also occurs if a faulty protein is been formed to eliminate the consequence of the protein formed by mistake.