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Protein Degradation quiz

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  • What is the main function of the proteasome in protein degradation?
    The proteasome is a multi-subunit protein complex that degrades proteins tagged with ubiquitin into short peptides.
  • What is ubiquitin and what role does it play in protein degradation?
    Ubiquitin is a small, 76-amino acid protein found in all eukaryotes that tags proteins for degradation by the proteasome.
  • What are the five main steps of the ubiquitin-proteasome pathway?
    The steps are: ubiquitin activation by E1, conjugation to E2, transfer to the target protein by E3 ligase, recognition by the proteasome, and degradation within the proteasome.
  • Which enzyme is responsible for activating ubiquitin in the first step of the pathway?
    The E1 ubiquitin-activating enzyme is responsible for activating ubiquitin.
  • What is the role of the E3 ubiquitin ligase in the ubiquitin-proteasome pathway?
    E3 ligase attaches ubiquitin to the target protein and is responsible for substrate specificity, recognizing which proteins should be degraded.
  • How does the proteasome degrade proteins after they are tagged with ubiquitin?
    The proteasome unfolds the ubiquitinated protein and feeds it through a cylindrical channel, where it is chopped into short peptides by ATP-dependent proteases.
  • What is the main difference between the lysosomal and proteasomal pathways of protein degradation?
    The lysosomal pathway does not require ubiquitin tagging; proteins are directly transported into the lysosome and degraded by proteases.
  • What is autophagy and how is it related to protein degradation?
    Autophagy is a process where cellular components, including proteins, are broken down in the lysosome, especially during cell stress or nutrient scarcity.
  • Why is protein degradation important for cellular regulation?
    Protein degradation controls protein levels in the cell, influencing cellular functions and maintaining homeostasis.
  • What can happen if misfolded proteins are not properly degraded?
    Misfolded proteins can aggregate in the cell and cause diseases or cellular dysfunction.
  • How does the cell recognize when a protein has reached the end of its lifespan?
    Proteins often have internal degradation signals that are exposed by conformational changes, triggering their degradation.
  • What energy source is required for the ubiquitin-proteasome pathway?
    ATP is required for both ubiquitin activation and the proteasome's protein-degrading activity.
  • How does the lysosomal pathway respond to changes in nutrient levels?
    The lysosomal pathway can rapidly degrade proteins in response to nutrient scarcity or external signals.
  • What is the fate of proteins degraded in the lysosome?
    Proteins are broken down into free amino acids by proteases within the lysosome.
  • Why are there many different E3 ligases in the cell?
    Each E3 ligase recognizes and targets different substrate proteins for ubiquitination, providing specificity to the degradation process.