protein modification

Question 1

functions of ER?

Answer 1

insertion of proteins into membranes

glycosylation

form S-S bonds

proper folding of proteins

proteolytic cleavage

Question 2

why is glycosylation important?

Answer 2

for correct protein folding
stability
facilitates interactions w/ other molecules

Question 3

explain N-linked Glycosylation

Answer 3

carbohydrate added by N-glucosyl link to amide Nitrogen of Asn

occurs in ER, further sugar modification in ER and golgi

oligossacharides preassembled on lipid carrier

Question 4

explain O linked glycosylation

Answer 4

carbohydrate added via glycosidic link to hydroxyl of Ser or Thr

occurs in golgi

important for proteoglycans

components of extracellular matrix and mucus secretion

Question 5

what is constitutive secretion from a cell?

Answer 5

continuous process

proteins packed in vesicle and released continuously via exocytosis e.g collagen

Question 6

what is regulated secretion form a cell?

Answer 6

proteins released in response to a signal, hormone

proteins in vesicles but not released until stimulus received e.g insulin

Question 7

how is protein imported into mitochondrial matrix?

Answer 7

protein w/ signal kept unfolded by chaperons

signal bind receptor

protein fed through pores in outer membrane

protein moves through channel in adjacent inner membrane

targeting signal cleaved

Question 8

explain process of protein synthesis and localisation to lumen of ER

Answer 8

protein synthesis initiated on free ribosomes
N-terminal signal sequence produced
sequence recognised by signal recognition particle

GTP bound SRPs directs ribosome making protein to receptors on systolic face of ER

SRP dissociates
synthesis continues, polypeptide fed into ER via pore
signal sequence removed
ribosome dissociates and recycled

Question 9

why is the C peptide bond an accurate measure of insulin in the blood?

Answer 9

C peptide is released when when an insulin molecule is being modified to mature insulin