Question

Q1. A member of the heat-shock class of proteins, BiP, is necessary for the proper folding of proteins in the ER. In terms of function, what do BiP and the heat-shock proteins (HSP) have in common?

Q2. Imagine a transmembrane molecule that lies in the plasma membrane and acts as a receptor for an extracellular signaling molecule. When the ligand-binding domain is inserted into the ER during synthesis of this transmembrane molecule, will it lie on the lumen side of the ER or the cytoplasm side?

Answer 1

Q1. Binding immunoglobulin Protein (BiP) is an HSP70 protein - family member and is involved in the folding and assembling of proteins in the Endoplasmic Recticulum (ER). BiP can actively fold proteins or simply bind and restrict protein from folding or aggregating. BiP also helps to import protein to the ER lumen or ER membrane (ATP-dependent).

Heat Shock Protein (HSP) prevent damage to the cell when exposed to conditions that cause protein unfolding and they stabilize new proteins to ensure correct folding. They also prevent unwanted protein aggregation. HSP aid in transporting proteins across membranes within the cell.

Q2. The ligand - binding domain will lie within the lumen of the ER.