What happens to proteins in the endoplasmic reticulum? Where do they go after?
There are two protein synthesis systems in any living eukaryotic cell: the free ribosome of cytoplasm and rough endoplasmic reticulum. When we talk about protein synthesis we mean only rough reticulum. But in generally it consist of tubules, vesicles and cisternae connected in wide network. Rough EPR additionally has a huge number of the ribosome connected to his structures. The main role of rough EPR unlike to free ribosome is synthesis of proteins that will be exported out of cell. It may be hormones, connective tissue parts (collagen protein), enzymes and other. The ribosome of EPR produces protein (it names translation) and then it placed to cistern of EPR. Then posttranslational modifications happen with protein. Firstly it is folding (making of protein secondary structure), then some structural changes, attaching some functional groups or molecules, modifications to the amino-acids included to the primary protein structure. All of these modifications are extending range of protein functions and helps him to achieve his final destination – place where protein will be functioning. After this procedures a vesicle with portion of mature proteins separates from EPR and shuttles them to Golgi apparatus, which main function to transport substances.