Lecture 12 Flashcards
What is essential for proper functioning cell?
protein degradation
What are some characteristics of protein degradation?
- highly controlled
- can be used as a way of regulation
- is executed bu proteases
Where are transmembrane proteins degraded?
lysosome
Where are cytoplasmic proteins degraded?
the proteosome
What is ubiquitin? Ub
small 76aa protein
What is the function of Ub?
a tag in protein degradation
Where is the C-terminus of Ub covalently linked to?
lysine side chainof proteins that suppose to be degraded
What are poly Ub chains?
proteins destined for degradation are often tagged not only by a single Ub but by poly Ub
What is E1
ubiquitin activating enzyme
What is E2
Ubiquitin-conjugating enzyme
What is E3
ubiquitin ligase
What are proteasomes?
large protein complex that degrades poly ubiquitinated proteins
How does the proteasome degrade the polyubquitinated protein?
- the cap unfolds the protein and feed the protein into the core
- the core cleaves the protein into small peptides
What is the proteasome responisble for?
the degradation of soluble proteins both in cytoplasm and nucleus
What happens in the MVB pathway?
- cell surface protein x is ubiquinated
- x-Ub is sorted in clathrn-coated vesicles and endocytosed
What is the X-Ub sorted by at the MVB?
ESCRT in the intralumenal vesicles
What happens after the X-Ub is sorted by the ESCRT?
- the MVB fuses with the lysosome and delivers the vesicles into the lumen of the lysosome
- the lysosome degrades the vesicles with their content (protein x)
How many ESCRT complexes are there?
5
Characteristics of ESCRT?
soluble cytoplasmic protein complexes
After being recruited by MVB, what happens to the ESCRT?
assembles into a machine that sort ubiquinated cargo and forms vesicles
What happens during ESCRT vesicle formation?
the membrane deforms away from the cytoplasm, even though the ESCRTs localize to the cytoplasmic face of the endosome
What is unique about ESCRT vesicles?
reversed topology
What happens to the membrane when the endocytic vesicles form with the help of a cthrn coat?
membrane deforms towards the cytoplasm
Where are MVB vesicles and their content degraded?
in the lysosome
What is Autophagy?
degradation of large particles and structures
What is autophagy induced by?
starvation
Why does starvation cause autophagy?
starvation causes degradation of cytoplasmic protein by autophagy which release amino acids important to survive the starvation conditions
How many membranes do autophagosoms have?
2 membranes
What do autophagosomes fuse with?
The lysosome and the content degraded
Steps of mitophagy?
- double membrane surround organelle
- organelle containing autophagosome fuses with lysosome
Autophagosome deliver their content to the —-
lysosome
What is the phase responsible for cell division?
M pahse
What phases are part of interphase?
G1 + S + G2
What are the responsibility of CDKs?
Phosphorylate proteins that are responsible for initiating and regulating the major events of the cell cycle
How are CDKs activated?
By binding to cyclin
What are cyclin ubiquinated and degraded by?
proteosome
