Explain the roles of the rough endoplasmic reticulum and the Golgi apparatus in protein trafficking and modification.

Proteins are produced at the ribosome. Ribosomes dock to the rER membrane on translocons and peptide is inserted into the rER lumen coupled with ATP hydrolysis. The peptide folds into its tertiary structure in the rER lumen and the protein is packaged into a vesicle. Vesicles have v-SNARES specific to t-SNARES on the cis-Golgi network. Upon receptor/ligand interaction, vesicle fuses with cis-Golgi network releasing protein into the lumen. The protein is modified/glycosylated within the Golgi apparatus. The Golgi apparatus also forms lysosomes and vesicles destined for secretion.