Lecture 15 - Protein turnover in epithelia Flashcards
What is protein half-life?
The time that half of the original population of protein remains. Or the time that half of the original population of protein has been degraded.
What does the lifetime of a protein depend on?
Lifetime of a protein depends on the function of a protein and the cellular pathway it is involved in.
Where are protein degraded?
In the lysosome or the proteasome
Why do we have the degradation of proteins? (5)
– to regulate the function/activity of a protein and therefore the cell.
– to allow replacement with new proteins.
– to inactivate them
– to recycle amino acids of nonfunctional proteins
– as they are extracellular proteins from pathogens.
What do lysosomes break down?
Extracellular or transmembrane proteins brought into the cell by endocytosis
Aged or defective organelles
What do lysosomes contain?
Enzymes (acid hydrolases) that break down proteins, sugars and nucleic acids
What do acid hydrolases work best in?
Acidic pH (not in cytosol).
How is low pH maintained in the lysosome?
Two transport proteins pump H+ and Cl- into the lysosome
to maintain a low pH.
What are the steps of autophagy? (5)
- Uptake of random area of cytoplasm or defective organelles (phagophore)
- Phagophore forms a complete ‘vesicle’ (autophagosome)
- Autophagosome begins to fuse with lysosome
- Autolysosome formed, degradation begins
- Organelles and any uptake substances degraded and recycled
What does ubiquitin signal?
Degradation
Endocytosis (monoubiquitin)
Changing location of a protein
What do deubiquitinating enzymes (DUBs) do?
Remove ubiquitin from proteins
What is E1 in ubiquitin-proteasome pathway?
Activating enzyme
What is E2 in ubiquitin-proteasome pathway?
Conjugating enzyme
What is E3 in ubiquitin-proteasome pathway?
Ligase
What happens in the ubiquitin-proteasome pathway?
E1, E2 and E3 enzymes catalyse covalent attachment of ubiquitin to target proteins.
