Functions of the Endoplasmic Reticulum Flashcards
What is Protein disufide isomerase (PDI) ?
It is an ER lumenal oxidoreductase that catalyses redox reactions that alter the positions of disufide bonds on proteins
Why is the process essential?
This process is essential for correct folding of proteins and for functionality of some lysosomal proteins and external domains of proteins
What do Disulfide bonds form between ?
Cysteine amino acids & the reducing environment of the cytosol prevents remote cysteine residues from interacting and forming these bonds
What environment is ER lumen?
ER lumen is an oxidative environment, so disulfide bonds can form
Explain Glycosylation ?
- Many proteins that enter the ER are glycosylated
- preformed branched oligosaccharide added en bloc to an Asparagine (N) residue
- Happens in the ER lumen so only extracellular parts of protein are glycosylated
ER is a major of site of ?
Protein synthesis
ER performs ‘quality control’ on ?
Protein folding
Properly folded proteins exported from ?
The ER to the Golgi apparatus
Improperly folded proteins held in ?
The ER by chaperone proteins until they are properly folded or, if this doesn’t happen, degraded
Heat shock proteins were characterised due to ?
The phenotypes of cells under heat shock
BiP/Kar2p is also involved in?
The stress response signalling and ER associated degradation
Explain quality control in ER ?
- N linked glycosylation
- Calnexin and Calreticulin cycles
- When trimming is wrong and folding is wrong proteins are targeted to proteasome for degradation
Unfolded proteins in the ER trigger ?
Production of chaperones and the expansion of the ER
Transmembrane receptors in the membrane activate?
A transcription factor in the cytoplasm when bound to unfolded proteins
What is the function of the smooth ER ?
The smooth ER is a major store of intracellular Ca2+
