Rough endoplasmic reticulum in the retina of a fruit fly

Transmission electron micrograph showing the rough endoplasmic reticulum (RER) from a drosophila retina. The rough endoplasmic reticulum is a folded organelle that is responsible for protein synthesis. It is distinguished from the smooth endoplasmic reticulum (site of vesicle production) by its characteristic 'rough' texture caused by the presence of ribosomes along its length.