Final answer:
Complex proteins for organelles are synthesized on ribosomes associated with the rough endoplasmic reticulum, where they undergo initial modifications. They are then packaged into vesicles and sent to the Golgi apparatus for further processing. Afterwards, they are delivered to the appropriate organelles or secreted from the cell.
Step-by-step explanation:
Pathway of Complex Protein Synthesis for Organelles:
The pathway to make complex proteins that become parts of organelles involves several steps and cellular structures. Initially, proteins are synthesized by ribosomes. If these proteins are targeted for organelles or secretion, they are synthesized by ribosomes on the rough endoplasmic reticulum (RER). Here, they enter the RER lumen and undergo structural modifications, such as folding or acquiring side chains. After the initial modifications in the RER, the proteins are packaged into vesicles and transported to the Golgi apparatus for further modification and packaging. Proteins destined for lysosomes, for example, are tagged with specific molecules that direct their transport. Eventually, the mature proteins are delivered to their respective organelles or are secreted from the cell. In addition to protein synthesis, the RER is involved in the production of phospholipids for cellular membranes. Proteins that are synthesized in the cytosol and destined for organelles such as mitochondria, chloroplasts, or the nucleus, contain specific signaling sequences that direct them to their intended destinations inside the cell. Overall, the endomembrane system, which includes the RER, Golgi apparatus, and various types of vesicles and lysosomes, works together to ensure proteins are correctly synthesized, modified, and routed to their destination, thereby playing a crucial role in the functionality and survival of eukaryotic cells.