12. Targeting and Modifying Proteins Flashcards
How is insulin secreted?
Regulated secretion.
What is collagen produced by?
Fibroblasts in connective tissue.
What is the basic unit of collagen?
Tropocollagen.
What is the structure of tropocollagen?
300nm rod shaped protein. 3 polypeptide a chains, each 1000amino acids long. Glycine is every third amino acid. It had a triple helix.
What are three factors of collagen’s triple helix structure?
It’s non-extensible, non-compressible and has high tensile strength.
How is collagen synthesised in the ER?
Synthesis and entry of chain into lumen of rough ER.
Cleavage of signal peptide.
Hydroxyl action of selected proline and lysine residues.
Addition of N-linked oligosaccharides.
Addition of galactose to hydroxylysine.
What is the purpose of prolyl hydroxylase?
It allows hydrogen bonding to stabilised the treble helix of collagen.
How is collagen modified in the ER?
Chains are aligned and disulphide bonds form.
The triple helix forms from C to N-terminus.
Glucose added.
Transport vesicle helps it exocytose.
N and C-terminal propeptides are removed.
How is pro collagen converted to tropocollagen?
Using pro collagen peptidases, extracellular.
How is a collagen fibre formed?
N and c-terminal propeptides are removed.
Lateral association of collagen molecules then covalent cross linking.
There is aggregation of fibrils.
What happens in the ER for insulin?
Disulphide bonds form.
What enzymes does proteolytic processing of insulting require?
PC3 endoprotease, PC2 endoprotease and carboxypeptidase.
How is collagen secreted?
Constitutive secretion.
