1) How do ER resident proteins remain in the ER? List some examples and describe the mechanism by which these proteins return the ER if they leave via the secretory pathways

2) What is the molar solubility (in mol L-1) of a salt with general molecular formula MX (where M is a cation and X is an anion) in a solution already containing 0.621 mol L-1 X- ? The Ksp of MX = 9.49 x 10-10 ?

Answer:

1.

ER-resident proteins are meant to stay in the endoplasmic reticulum since they have a KDEL sequence which is a unique amino acid sequence found at the C terminal end of the amino acid chain and it acts as a signal recognition (SRP) that in short the protein is maintained inside the endoplasmic reticulum.

The Examples are heat shock protein (HSP 70) chaperon BiP/Kar2.

The secretory pathway -

The secretory proteins are targeted to the endoplasmic reticulum through COP -1, which is also known as a retrograde pathway. COP-1 vesicles move from cis Golgi to RER using ADP ribosylation factor(ARF). KDEL in the ER lumen-specific signal containing protein that binds with its specific receptor in the lumen of the cis Golgi and this process requires a slightly acidic environment. KDEL containing protein detaches from its receptor in RER lumen at neutral pH.

The binding of Rab to its effector is called vesicle docking. The binding of V-SNARE to T- SNARE is called membrane fusion.

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