What Is Endoplasmic Reticulum

Endoplasmic reticulum (ER) , in biology , a continuous membrane system that forms a series of flattened sacs within the cytoplasm of eukaryotic cells and serves multiple functions, being important particularly in the synthesis, folding, modification, and transport of proteins . All eukaryotic cells contain an endoplasmic reticulum (ER). In animal cells, the ER usually constitutes more than half of the membranous content of the cell . Differences in certain physical and functional characteristics distinguish the two types of ER, known as rough ER and smooth ER.