Transmission Electron Micrograph (TEM) of rough endoplasmic reticulum, showing the stacked arrangement of the channels of rough endoplasmic reticulum. Its granular appearance is due to the presence of ribonucleic acid (RNA) and proteins in the form of ribosome subunits studded along the surface. Proteins are made on these ribosomes and assembled within the endoplasmic reticulum and from there are transported to the next processing step until they are complete protein packages. Magnification: 30,000x @ 8 x10 inches.