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🔬general biology i review

Polyubiquitination

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

Polyubiquitination is the process in which multiple ubiquitin molecules are attached to a protein, marking it for degradation by the proteasome. This post-translational modification plays a crucial role in regulating protein turnover and signaling pathways, ensuring cellular homeostasis and response to stress or damage.

5 Must Know Facts For Your Next Test

  1. Polyubiquitination typically involves the attachment of ubiquitin molecules in a chain formation, usually linked through lysine 48 of the first ubiquitin, signaling the protein for destruction.
  2. This process is critical for various cellular functions, including cell cycle regulation, DNA repair, and immune responses.
  3. The enzymes involved in polyubiquitination include E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3 (ubiquitin ligase), with E3 playing a key role in determining substrate specificity.
  4. Defects in polyubiquitination pathways can lead to diseases such as cancer and neurodegenerative disorders due to the accumulation of damaged or misfolded proteins.
  5. The reverse process, deubiquitination, can remove ubiquitin chains from proteins, allowing them to escape degradation and regulate their activity or stability.

Review Questions

  • How does polyubiquitination influence cellular processes and protein regulation?
    • Polyubiquitination is essential for maintaining protein homeostasis by marking unwanted or damaged proteins for degradation via the proteasome. This process helps regulate various cellular functions such as the cell cycle, stress responses, and apoptosis. By controlling protein levels through polyubiquitination, cells can effectively manage their internal environment and respond to changes or damage.
  • Discuss the role of E3 ligases in the polyubiquitination process and how they affect substrate specificity.
    • E3 ligases are crucial enzymes in the polyubiquitination process as they facilitate the transfer of ubiquitin from an E2 enzyme to a substrate protein. They play a significant role in determining which proteins get ubiquitinated by recognizing specific degradation signals on substrates. This specificity is vital because it ensures that only certain proteins are targeted for degradation based on cellular conditions or stress signals.
  • Evaluate the consequences of impaired polyubiquitination on cellular health and disease development.
    • Impaired polyubiquitination can have serious consequences on cellular health, leading to the accumulation of damaged or misfolded proteins that can disrupt normal cellular functions. This dysfunction is associated with various diseases, including cancer, where tumor suppressor proteins may fail to be degraded, allowing uncontrolled cell growth. Additionally, neurodegenerative diseases such as Alzheimer's involve disrupted protein turnover due to faulty ubiquitin-proteasome pathways, highlighting the importance of proper polyubiquitination in maintaining cellular integrity.