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Quality Control

Quality Control. Key Questions. How is protein “quality” controlled? two types of medical problems: proteins that are OK but degraded proteins that aggregate & are not degraded. Overview. Part 1. ER Processing Reactions.

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Quality Control

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  1. Quality Control

  2. Key Questions How is protein “quality” controlled? two types of medical problems: proteins that are OK but degraded proteins that aggregate & are not degraded

  3. Overview

  4. Part 1. ER Processing Reactions

  5. Post-translational modifications and quality control in the rough ER • Newly synthesized polypeptides in the membrane and lumen of the ER undergo five principal modifications • Formation of disulfide bonds • Proper folding • Addition and processing of carbohydrates • Specific proteolytic cleavages • Assembly into multimeric proteins

  6. Disulfide bonds are formed and rearranged in the ER lumen Figure 17-26

  7. En bloc transfer from dolichol to NXS/T

  8. Different structures characterize N- and O-linked oligosaccharides Figure 17-30

  9. The immediate precursors in the synthesis of oligosaccharides are nucleoside diphosphate or monophosphate sugars Figure 17-31

  10. Specific sugars are linked by specific glycosyltransferases Figure 17-32

  11. ABO blood type determined by two glycosyltransferases Figure 17-34

  12. Building the dolichol donor involves flipping

  13. Addition and initial processing of N-linked oligosaccharides in the rough ER Figure 17-36

  14. Part 2. Chaperones

  15. Efficient Folding Avoids or Transits Local Minima

  16. Chaperone Cycle

  17. Correct folding of newly made proteins is facilitated by several ER proteins Figure 17-27

  18. Glucosyltransferase Discriminates Folded from Unfolded

  19. Part 3. Unfolded Protein Response

  20. Many genes induced by UPR

  21. UPR Induction Pathway

  22. Part 3. Proteasome-mediated degradation

  23. Retrotranslocation, then Ubiquitinylation then degradation in Proteasome

  24. Ubiquitin Structure

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