Protein Processing And Targetting Flashcards
(9 cards)
What is constitutive secretion?
Continuous pathway
Protein packaged in to vesicles and released continuously by exocytosis
What is regulatory secretion?
Proteins released in response to a signal. Packaged into vesicles and released when stimulus is received
Overview of protein secretion pathway
PS initiated on free ribosomes –> N terminal sequence produced –> signal sequence recognised by SRP –> PS stops –> GTP bound SRP directs complex to SRP receptors on ER membrane –> SRP dissociates –> PS continues –> protein enters through pores –> signal sequence removed –> ribosome dissociates –> protein folds
Modifications in ER ?
Signal cleavage
Disulfide bond formation
N linked gylcosylation
Modifications I’m Golgi body?
O linked glycosylation
Trimming and modification of n linked oligosarrcharides
Further proteolytic processing
How is insulin synthesised?
Inactive single polypeptide chain containing signal sequence, A, B and C peptides
Signal sequence cleaved by signal peptidase and 3 disulfide bonds formed
Endopeptidase removes C peptide
Therefore insulin contains A+B peptides joined by 2 disulfide bonds and c is released
C= good way of measuring endogenous insulin in diabetes
Describe tropogcollagen
300 nm rod shaped protein
Primary sequence = XY Gly
3 a- chains make a right handed helix
Which has high tensile strength
What is collagen synthesised as?
Pre procollagen
Overview of collagen biosynthesis
Synthesis + entry of chain into rER –> cleavage of signal peptide –> hydroxylation of selected proline+ lysine residues –> addition of n-linked oligosaccharides –> addition of galactose tonhydroxyproline residues –> chain alignment and disulfide bond formation –> formation of triple helical procollagen from C to N terminus –> to golgi –> o linked glycosylation –> asked into transport vesicles –> exocytosis –> removal of N and C terminal propeptides –> lateral aggregation to form fibrils
