Final answer:
Misfolded proteins are prevented from entering the COP-II site by chaperone proteins such as HSP70, and are targeted for degradation through a process that tags them with ubiquitin.
Step-by-step explanation:
What Prevents Misfolded Proteins from Entering the COP-II Site?
Proteins that are misfolded are typically kept from the COP-II site by a quality control system involving chaperone proteins like HSP70. These chaperones assist in the proper folding of proteins and prevent them from aggregating. When proteins are incorrectly folded, they are targeted for degradation by a process involving ubiquitin, which tags the misfolded proteins for destruction at the proteasome.
Both the HSP70 chaperone and ubiquitin systems ensure that only properly folded proteins are transported by COP-II. These mechanisms are crucial for maintaining cellular function and preventing the accumulation of dysfunctional proteins.