The synthesis of proteins from mRNA templates, a process known as translation, takes place in two primary locations within eukaryotic cells. Ribosomes, the molecular machines responsible for this synthesis, can be found either freely floating in the cytoplasm or bound to the endoplasmic reticulum. Consequently, protein production occurs in both the cytosol and on the surface of the rough endoplasmic reticulum.
The location of protein creation is determined by the protein’s ultimate destination. Proteins destined for use within the cytoplasm, or targeted to organelles such as the mitochondria or nucleus, are typically synthesized by ribosomes in the cytosol. Conversely, proteins intended for secretion from the cell, insertion into the plasma membrane, or delivery to organelles within the endomembrane system (e.g., the Golgi apparatus, lysosomes) are generally produced by ribosomes attached to the endoplasmic reticulum. This compartmentalization allows for efficient protein sorting and delivery to their correct locations.
