Final answer:
Misfolded proteins are targeted and ubiquitinated in the cell, then transported by chaperone proteins such as HSP70 to the proteasome, where they are digested into peptides and amino acids. Chaperones assist in crossing membranes, making it possible for proteins to be degraded in the cytoplasm.
Step-by-step explanation:
The process of degrading misfolded proteins in the cytoplasm involves a series of steps, starting with the targeting by ubiquitin. This 76-amino acid polypeptide marks the protein for destruction, signaling it to be delivered to the proteasome, which is a large complex responsible for proteolysis. However, misfolded proteins cannot directly cross membranes; they require chaperone proteins such as HSP70 to assist in their transport and unfolding.
Once in the cytoplasm, the protein is directed to the proteasome where it is digested into peptide fragments. The fragments are then released and further broken down into free amino acids. It is noteworthy that there are hundreds of ubiquitin molecules, each specific to different types of proteins, facilitating highly selective targeted destruction.
Additionally, lysosomes also play a role in protein turnover by internalizing extracellular and intracellular proteins which are then degraded by proteases known as cathepsins.