Talk about the proteins synthesis role of RER.

Secreted proteins and proteins of the endomembrane system are synthesized by ribosomes attached to the RER cotranslationaly delivery, all other proteins in cells are synthesized by free ribosomes with posttranslational delivery. Protein synthesis is catalyzed by a signal sequence with the help of SRP, and the translocon will be inserting the growing polypeptide, after removing signal sequence into the lumen of the RER, each protein has an address code that makes the protein go to a specific place. Integral proteins are synthesized like other proteins, but translocon recognizes helix shaped hydrophobic aa chain, so the translocon captures it and retain it to be delivered to the lipid bilayer by lateral opening