Endoplasmic reticulum (ER) – the microfactory of cellular secretory peptides
Cellular peptides destined for extracellular secretion are synthesized by the ribosome unit associated with the ER membrane,
and further deposited in the ER lumen for additional processing. This high-magnification image of rough ER was taken from the
cytoplasm of a cultured fibroblast. Red arrows indicate several typical ribosomes on the cytosolic side of ER, and red stars
indicate the ER lumen which is filled with newly synthesized peptides. Peudo-color and labels added with Photoshop CS4.