[W10] The Proteosome and Autophagy Flashcards
(23 cards)
What is protein homeostasis?
The balance between protein production and degradation.
What two systems maintain protein degradation?
The proteasome and autophagy.
What are the lecture’s main focus areas?
Protein homeostasis, proteasome, ubiquitinylation, immune detection, and autophagy.
What determines a protein’s lifespan?
Its half-life (T½), influenced by post-translational modifications and protein ageing.
How common are translation errors compared to transcription errors?
About 10× more frequent – ~1 error per 10 proteins.
What is the role of molecular chaperones like Hsp60?
They help fold or refold misfolded proteins and prevent aggregation.
Where is the proteasome found?
In the cytosol and nucleus.
How much of cell protein can the proteasome make up?
Up to 1% of total cell protein.
How is proteasome production regulated?
Through signalling pathways responding to cellular needs.
What type of proteins does the proteasome degrade?
Misfolded, damaged, or unneeded proteins tagged with ubiquitin.
What is ubiquitin?
A small 76-amino acid protein used to tag proteins for degradation.
What enzymes are involved in ubiquitinylation?
E1: Ubiquitin-activating enzyme, E2: Ubiquitin-conjugating enzyme, E3: Ubiquitin ligase (adds ubiquitin to substrate).
What happens to ubiquitin-tagged proteins?
They are recognized by the proteasome, unfolded, and degraded into peptides.
Which tumour suppressor is regulated by the proteasome?
p53, which is targeted for degradation via ubiquitinylation.
What is autophagy?
A cellular process of self-degradation where damaged components are recycled.
What are the three types of autophagy?
Macroautophagy, Microautophagy, Chaperone-mediated autophagy (CMA).
What does mTOR do in autophagy?
Inhibits autophagy; its suppression activates autophagy during stress or starvation.
What triggers autophagy?
Nutrient starvation, cell stress, or accumulated damage.
How does autophagy assist the immune system?
By delivering intracellular antigens to MHC class II compartments for presentation.
What role does this play in immunity?
It helps distinguish between self and non-self antigens.
What is the main difference between the proteasome and autophagy?
The proteasome degrades small, tagged proteins, while autophagy degrades large aggregates and organelles.
How do chaperones assist both systems?
They help fold proteins and direct misfolded ones toward degradation pathways.
What’s the significance of these systems in ageing and disease?
Dysfunction in protein clearance contributes to ageing, neurodegeneration, and cancer.
