What are ribosomes that are fixed to the endoplasmic reticulum used for?

Ribosomes that are fixed to the endoplasmic reticulum, commonly referred to as rough ER, play a crucial role in the synthesis of proteins that are destined for export out of the cell or for incorporation into cellular membranes. This specialized function is essential for the production of a variety of proteins, including hormones and enzymes, that the cell needs to release into the extracellular environment or to integrate into its own structures.

During protein synthesis, the ribosomes translate mRNA into polypeptide chains, which are then pushed into the lumen of the rough endoplasmic reticulum. The rough ER facilitates the proper folding and post-translational modification of these proteins. Once properly folded, proteins can be packaged into vesicles and transported to the Golgi apparatus for further processing and eventual export from the cell.

In contrast, other functions related to cellular metabolism and maintenance—such as ATP production, degradation of damaged organelles, and transport across membranes—fall under the responsibilities of other organelles or cellular components. For instance, ATP production primarily occurs in mitochondria, while lysosomes are responsible for degradation processes. Membranes have specific transport proteins that facilitate movement rather than ribosomes, which focus exclusively on protein synthesis.