Within eukaryotic cells, the rough endoplasmic reticulum (RER) serves as the principal site for the synthesis of proteins intended for secretion, insertion into membranes, or delivery to lysosomes. Ribosomes attached to the RER translate messenger RNA (mRNA) into polypeptide chains. These nascent proteins enter the RER lumen, where they undergo folding and modifications, such as glycosylation, prior to their transport to the Golgi apparatus for subsequent processing and sorting.
The functions of other organelles are:
- Mitochondrion: Primarily responsible for ATP production via cellular respiration; does not synthesize secretory proteins.
- Golgi apparatus: Receives, modifies, packages, and sorts proteins from the RER for secretion or other destinations; not the initial site of protein synthesis.
- Lysosome: Houses hydrolytic enzymes for intracellular digestion; not involved in protein synthesis.
Consequently, the organelle most significantly involved in the synthesis of proteins designated for secretion is the rough endoplasmic reticulum.