Flashcards in Secretory Pathway and Intracellular Traffic Deck (22)
What are the 3 mechanisms of protein transport?
Nuclear transport (gated transport between cytosol and nucleus)
Transmembrane transport (across a membrane from the cytosol into an organelle through translocators - i.e. protein synthesis and mitochondrial import
Vesicular transport (membrane bound transport intermediates move proteins and lipids from one compartment to another)
What are the major organelles of exocytosis?
vesicles and tubules
What are the 6 major functions of the ER?
1. Synthesis of lipids (phospholipid, ceramide, cholesterol) - sER
2. Control of cholesterol homoeostasis (sensor and synthesis)
3. Storage of Ca+ (uptake and release)
4. Synthesis of proteins on membrane bound ribosomes - rER
5. Co-translational folding of proteins and early posttranslational modifications
6. Quality control
What is the function of BiP?
Binds proteins as they enter the ER and help them to fold properly => interact with protein disulfide isomerase and create disulfide bonds
What is SRP?
a Signal Recognition Particle
- 6 protein complex bound to 1 RNA molecule
What is the function of SRPs and how do they work?
recognizes ER signal sequence and directs newly formed proteins to ER
- binding pocket recognizes signal sequence
- SRP binding induces pause in translation until SRP receptor bound
- ribosome attaches to translocon
- SRP releases
What is a translocon?
protein channel allowing polypeptide chain to enter the ER
How are proteins with transmembrane domains (TMDs) synthesized
1. Single TMD "Type I membrane protein"
- mRNA contians stop transfer signal
- released by translocon- remainder synthesized on cytosolic face (either c terminal or amine terminal out)
2. multiple TMDs
- just internal stop and start to go back and forth across
- synthesized on correct side => made into membrane
Where does N-linked glycosylation occur?
in ER lumen when asparagine carbohydrate complex is added to membrane protein
What is the function of an asparagine carbohydrate group?
prevent protein aggregation (at hydrophobic domains)
tags to monitor unfolded proteins
What are vesicle coats made of?
soluble cytoplasmic proteins and lipids
How does COPII travel?
ER to golgi (forward)
How does COPI travel?
Golgi to ER (backward)
How does clathrin travel?
Golgi to plasma membrane
Name a protein that is recycled?
SCAP that bind SERBP
What is the function of SCAP & SCRBP?
regulate cholesterol synthesis and export from ER
What are the 4 major functions of the golgi aparatus?
1. Synthesis of comples sphingolipids from ceramide backbone
2. Additional post-translational modifications of proteins and lipids
3. Proteolytic processing
4. Sorting of proteins and lipids fro post-golgi compartments
What are the compartments of the golgi in order of increasing distance from the nucleus?
TGN - trans golgi network
Where does sulfation occur?
trans and TGN
Where does most glycosylation occur?
What does constitutive secretion mean?
Contents will be secreted immediately