Inside eukaryotic cells, misfolded proteins within the secretory pathway can be recycled by a quality-assurance mechanism. Arrange the steps in this process in their correct chronological order with the earliest step at the top. Instructions Ubiquitin is attached to defective protein. The tagged protein is recognized by the proteasome. Ubiquitin is released and recycled. The defective protein is cleaved into smaller peptides.
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This process involves ubiquitin tagging and proteasomal degradation. Show moreā¦
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ERAD, or ER-associated degradation, is a quality control measure with the following functions: A. Misfolded proteins activate the expression of genes such as chaperones that will help to refold and stabilize misfolded proteins until they fold correctly. B. Misfolded proteins are ubiquitinated and degraded by proteasomes inside the ER. C. By recognizing the structure of carbohydrates attached to proteins in the ER, incorrectly folded proteins are retained in the ER, allowing for multiple cycles of refolding. Proteins that cannot fold correctly are ejected from the ER through the translocon and degraded by the ubiquitin-proteasome system. D. Unfolded proteins in the ER activate a transmembrane kinase that phosphorylates misfolded proteins. These misfolded proteins are then sent to the lysosome in vesicles for degradation.
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Retrotranslocation of N-glycosylated proteins occurs simultaneously with protein folding by chaperones in the lumen of the endoplasmic reticulum. The oligosaccharide bound to the protein undergoes additional trimming of specific mannoses. Once one glucose is added back to the oligosaccharide bound to the protein by UGGT (UDP-glucose glycoprotein glucosyltransferase), two of the three glucoses of the original oligosaccharide bound to the protein are removed, and the protein is ubiquitinated.
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Misfolded proteins are directed to a protein machine called a _____ to be degraded.
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