ER Transport

Transmembrane proteins and Water-soluble proteins.

Synthesized in lumen and partly translocated, embedded into the membrane. Destined to stay in ER or plasma membrane proteins.

Translocated into the ER lumen and are desitined for lumen of organelle or secretion.

When the growing polypeptide is simultaneously translated by mRNA, it is translocated across the ER membrane.

When the polypeptide is translated by mRNA first and then translocated across the membrane. Needs chaperone proteins in the cytosolic side of ER.

Protein synthesis, has membrane bound ribosomes.

Produces lipids and steroids and cholesterol (contains cytochrome p450 family, makes water insoluble drugs soluble which are then excreted).

A method of anchoring proteins to the ER membrane. GPI is the anchor covalently bonded to the c terminus of a protein destined to be attached to the plasma membrane.

Retention signal near C terminus

PDI is protein disulfide isomerase, Catalyzes the oxidation of free sulfhydryl groups on cysteines to form disulfide groups. A kind of ER resident protein.

Chaperone protein that recognizes incorrectly folded proteins.

Golgi, lysosomes, membrane proteins, extracellular space.

Nlinked

Rough ER will synthesize the oligosaccharides on the cytosolic side, when synthesis of oligosaccharides occurs they add phosphate groups. During the synthesis process, the oligosaccharides are flipped to the lumenal side of the ER.

Ogliosaccharide chain is connected to ER membrane via a dolichol with a strong phosphate group. (phosphates are high in energy and needed for transfer to proteins)

Translocating protein on the cytosolic side of cell will dock at a oligosaccharyl transferase. The active site of OT is on the lumenal side of ER. The ogliosaccharide chain is transferred to cytosolic side and attached to asparaginine of translocated protein.

The signal or n terminus signal sequence of the translocated proteins is cleaved off by a peptidase embedded in the Rough ER membrane.

While the protein/polypeptide chain is being translated it has a signal sequence that binds to signal recognition particle.
The SRP binds to a SRP receptor embedded in the Rough ER membrane and opens the translocator.
The polypeptide chain enters while being translated and has its N terminus cleaved by the RER peptidase.