Insulin

Question 1

Give four ultrastructural features of B cells which make it specialised for insulin secretion

Answer 1

Extensive rough endoplasmic reticulu a well defined golgi apparatus many mitochondria a well defined system of microtubles and microfilaments.

Question 2

Give insulin synthesis up to disulphide bond formation

Answer 2

Synthesised as pre-proinsulin on ribosomes associated with rough endoplasmic reticulum Pre-part is a signal peptide which ensures newly synthesised protein enters cisternal space of the endoplasmic reticulum. Then removed.Remaining proinuslin folds to ensure correct alignment of the cysteine residues and the correct disulphide bonds

Question 3

Give synthesis and secretoon of insulin from disulphide bond formation

Answer 3

Proinsulin transported to golgi apparatus from ER and packaged into storage vesicles.Proteolysis in stroage vesicles removes a connecting peptide from near the middle of the chain.This breaks single chain into two chains held by disulphide bridge - mature insulin.Storage vesicle contain insulin and C-peptide in equimolar amounts. Entire contents realeased during secretion. Measurement of C-peptide useful marker of insulin secretion