Post-translational Processing of Proteins Flashcards
What is the function of ER?
Insertion of proteins into membranes, Specific proteolytic cleavage, Glycosylation: adding of sugar Formation of S-S bonds, disulphide bonds, Proper folding of proteins, Assembly of multi-subunit proteins, Hydroxylation of selected Lys and Pro residues
What is o-linked glycosylation and where does it occur?
Occurs in Golgi, Attachment of sugar to OH of serine, Important in proteoglycans = component of extracellular matrix and mucus secretions
How does an ER chaperone attempt to correct protein mis-folding?
retain unfolded proteins in the ER, act as sensors to “monitor” extent of protein mis-folding
How is preproinsulin processed?
- Enter ER: remove single peptide
- Disulphide bond forms
- Enter Golgi: endopeptidase remove B chain
- 2 C chains join
Where do proteins that are synthesised on free ribosomes go?
Cytosol or organelles
Where do proteins synthesised on ER go?
Membrane or secreted
What happens during post-translational modification?
Proteolytic cleavage and/or chemical modification
What happens when protein misfolding cannot be corrected?
Protein is sent to the cytosol for degradation or it may accumulate in the ER = toxic - disease
What is an ER chaperone?
Attempts to correct problems: will retain unfolded proteins in the ER, will act as a senior to monitor extent of protein misfolding = mediate reduction in transcription
what is the difference between constitutive and regulated secretion?
constitutive = all the time
regulated = turned on/off
why is glycosylation important?
correct protein folding, stability, facilitates interactions
What modifications happen in the golgi?
sorting, removal of Man, addition of NANA and Gal
why can proteolytic processing yield different amounts of products?
diff amounts of processing enzymes in diff cell locations
