1.1 The structure of Endoplasmic Reticulum (ER) ER is a network of membrane-enclosed tubules and sacs (cisternae)that extends from the nuclear membrane throughout the cytoplasm. ER is the largest organelle of most eukaryotic cells. Its membrane may account for about half of all cell membranes. The space enclosed by the ER may represent about 10%of the total cell volume. This document is produced by trial version of Print2Flash.Visit www.print2flash.com for more information