List four principle events that occur in the ER with regard to protein production and/or modifications? Solution The endoplasmic reticulum (ER) forms a network of tubules that are enclosed by membrane and sacs (cisternae) extending from the nuclear membrane throughout the cytoplasm. ER plays a critical role in protein processing and sorting. Some of the critical events that occur in ER are listed below; 1. ER acts as a port of entry of the protein secretory pathway. Proteins destined for the entry to cell wall or vacuole or for the other compartments of the cell, first enters into the ER and are then transported to the Golgi complex, from where they en route to final destination organelles. ER thus represents a major organelle involved for the traffic of proteins within eukaryotic cells. 2.Newly sunthesized polypeptides undergoes functional folding in ER. It is the organelle where many multimeric proteins assemble. Proteins are retained in ER until they acquire their correct final conformations. 3. It is in ER where the glycoproteins acquire their asparagine-linked glycans.Also, in some plant cells, ER is the site for aggregation and accumulation of some storage proteins. 4. Rough ER (RER) is the site for manufacture of secreted proteins,which are either secreted constitutively without any tag or secreted in a regulatory manner involving clathrin and paired basic amino acids in the signal peptide..