Final answer:
Proteasomes digest proteins that are specifically marked with a chain of ubiquitin, which serves as a signal for degradation. This ubiquitination ensures that only targeted proteins are degraded by the proteasome, maintaining cellular functionality.
Step-by-step explanation:
The student has asked a question related to the digestion of proteins by proteasomes. Proteasomes are complex structures responsible for degrading unwanted or damaged proteins within the cell. The basic process of degradation involves marking the proteins with ubiquitin, a small regulatory protein. Once a protein is marked with a chain of ubiquitin, it is recognized by the proteasome and targeted for destruction. This system helps maintain cellular health by removing proteins that are damaged or no longer needed.
To specifically answer the student's question, proteasomes only digest proteins that are b. marked with a chain of ubiquitin. This tagging process ensures that the degradation is highly selective and that only those proteins meant to be discarded are processed by the proteasome.