4 - The endoplasmic reticulum

What should you use to analyse radioactive proteins?

SDS-PAGE

What do SDS-PAGE do?

Separate by size

Where does post-translational modification of proteins occur?

In the ER

What is protein folding assisted by?

Molecular chaperones in ER lumen

Functional roles of N-linked glycosylation:

• Form the glycocalyx

• Can be mod into mannose 6 phosphate

• assist protein folding

What is BiP?

ATPase

What does BiP do?

Binds exposed hydrophobic residue

What does Calnexin do?

Bind N-glycosylated proteins

What are all the ways proteins can be modified in the ER?

1. Signal sequence cleavage

2. disulphide bond formation (oxidation)

3. Glycosylation

What is glycosylation?

Covalent attachment of carbohydrate

How is a disulphide bond formed?

Oxidation of cysteine side chains / cat. by protein disulphide isomerase inside ER lumen

What does mannose-6-phosphate tags act as?

Lysosome sorting signal

What is the glycocalyx?

Protective layer outside eukaryotic cells / carbohydrates attached to proteins and lipids.

Where is the Glycocalyx made?

ER / Golgi

ER size & function is controlled by______?

Demand

What does the build up of misfolding proteins in ER lumen trigger?

Unfolded protein response

What triggers the unfolding protein response?

Build up of misfolded proteins in the ER lumen

What determines the arrangement of transmembrane proteins in the lipid bilayer?

Additional hydrophobic signal sequences

What acts as the entry point for the secretory pathway?

The ER

Proteins that cannot fold correctly are retained by_________?

ER quality control

What does UPR stand for?

Unfolded protein response

What is the function of chaperones in quality control?

Chaperones bind to misfolded proteins and stops them leaving the ER quality control