2. The structure and functions of Endoplasmic Reticulum(ER) inner nuclear membrane ER membrane nucleus outer nuclear membrane polyribosome RER has ba ribosomes on the cvtosolIc de of continuous flattened sacs (cisternae): A) 200nm 400nm SER IS an 5(B) rough ER smooth印R Interconne cting network of tubular membrane elements o0 nm ER lumen2. The structure and functions of Endoplasmic Reticulum(ER)