Final answer:
The protein degradation of misfolded proteins is achieved by tagging them with ubiquitin, which flags them for breakdown at the proteasome.
Step-by-step explanation:
Protein degradation of misfolded proteins is accomplished d) by tagging these proteins with small ubiquitin proteins that form a polyubiquitin chain. This process involves the addition of an ubiquitin group to a protein, which marks it for degradation. Ubiquitin acts as a signal that a protein's lifespan is complete. The tagged proteins are then transported to the proteasome, an organelle responsible for breaking down proteins.
The ubiquitin-proteasome pathway is essential for maintaining cellular homeostasis by regulating protein turnover. This system involves multiple enzymes, such as ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), and ubiquitin ligases (E3). Among these, E3 ligase confers specificity to the degradation process, targeting specific proteins for the polyubiquitin tagging. The ubiquitin-tagged proteins are recognized by the proteasome, which procedurally digests the proteins into shorter peptide fragments and then further degrades them into free amino acids.