Polvi lec #10 Flashcards
What do you call proteins that have become gycolsylated?
glycoproteins
Do majority of the proteins at the rough er become glycosylated?
yes
What do the carbohydrate groups do for proteins?
They have roles as binding sites, they aid in folding and stabilization of proteins, they help with making the protein more soluble, and carbohydrates can help sort/direct proteins to diff cellular compartments
What are the two types of glycosylation?
N-linked and O-linked
What is N-linked glycolysation?
the sugar is nitrogen linked to asp of the protein, this is initiated in the RER
What is O-linked glycolysation?
The sugar is linked to the protein by an oxygen bond and is linked to the protein by serine, this occurs in the golgi
How does N-linked glycolysation work?
Initial assembly is on the cytosolic side, seven sugars are transferred one at a time (through glycosol tranferase) to the lipid molecule dolichol pyrophosphate which is embedded in the ER
Dolichol and attached sugars are flipped across the membrane
the rest of the sugars are attached to the dolichol on the cytosolic side and then are flipped and added to the growing previous chain
the competed oligosaccharide is transferred to asn of polypeptide that’s being translated by the enzyme oligosaccharyltransferase (the sequence of amino acis is asn-x-ser/thr)
Before proteins exit RER and go to golgi, how does quality control for misfolded proteins work?
Glucosidase 1 and 11 remove two glucoses, leaving one single glucose on protein, this allows it to recognized by Calnexin (a chaperon protein that helps folding), another glucose gets removed and that frees protein from calnexin
UGGT (an enzyme) recognizes incompletely folded proteins by detecting hydrophobic residues and adds a glucose molecule
glycoprotein gets checked by calnexin again is incompletely folded
If not, the folded protein exits the cell
Say after all the quality control, calnexin can’t fold it right and UGGT detects improper folding but nothing can be done, what happens?
The improperly folded proteins are degraded in a proteosome in the cytosol
How do proteins exit the ER?
- Membrane vesicles with enclosed material bud off ER
- Vesicles fuse with one another to form larger vesicles (called vesicle tube carriers) in the ERG (endoplasmic reticulum golgi intermediate compartment)- is the space between the ER and golgi
How is the golgi complex structured?
Have cisternae arrange dina stack, cis cisternae are closer to RER, then medial, than trans (fruthest from RER)
What is the trans-golgi network?
is above trans cisternae, furthest from RER, is tubules and vesicles that act as a sorting staion where proteins get sorted into diff vesicles
What is the cis-golgi network?
is a network of tubules, is closest to RER, and sorts between proteins that need to be returned to the ER and those that should proceed to the golgi
What modifications happen in the Golgi complex?
O-linked glycoproteins are made in golgi
the order that the proteins gets glycosylated depends on the location of specific glycotransferases in the membrane of the golgi complex
N-linked carbohydrate chains can also be modified here
What are the models for movement of materials through the golgi complex?
The vesicular transport model- says that comoartments of golgi are stable and vesicles bud off compartments and go to the next
The cisternal maturation model- says that cisternae for near ER (at cis face) and move towards the trans face as they mature
The cisternal one more likely
