Cellular protein synthesis. Illustration of the synthesis of proteins in cells on the membrane system called the rough endoplasmic reticulum. This is a bilayer membrane (light blue) with receptor proteins (light and dark blue) embedded in it. Ribosomes (orange) are where the proteins (purple chains) are produced. The ribosomes attach to the receptors, and the proteins pass across the membrane into the lumen of the rough endoplasmic reticulum. Here, sugars (pink) attach to the proteins, forming glycoproteins (upper right). For this artwork with labels, see image C023/8741.