Endoplasmic reticulum

The outer membrane of the nucleus is in places continuous with a complex, three-dimensional array of membrane tubes and sheets, the endoplasmic reticulum (ER). Tubular ER can be studded with ribosomes, and described as rough ER (RER), where ribosomal translation and protein modification take place. These proteins can either be secreted into the lumen of the ER or inserted into the membrane. Plates of smooth ER are associated with lipid synthesis and protein and lipid transport across cells.