Protein Processing And Targetting Flashcards
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
