How do the rough Endoplasmic Reticulum and the Golgi Apparatus act in the production and releasing of proteins?

The Rough
Endoplasmic Reticulum(RER) is involved in the production of proteins. ie., on the membrane of
RER, large numbers of ribosomes are attached. The ribosomes are the actual sites for protein
synthesis. The ribosomes attached to the RER are involved in the synthesis of proteins that are
meant to be transported outside the cell (ie., secreted) like several enzymes.

The ribosomes on RER synthesise the proteins and release them into the lumen of RER.
After processing and folding, the proteins are packaged into vesicles called "transition
vesicles" which are formed by the RER membrane getting pinched around the cargo. These
transition vesicles then move towards the Golgi apparatus.

Once they reach
the Golgi body, the transition vesicles enter it through the cis side of Golgi body by merging
with the Golgi stacks. Within the Golgi body (or apparatus), the proteins undergo further
processing, concentrating and also a tagging. The tag determines the target location and the
function of the processed protein. Then the protein gets trafficked through the Golgi stacks and
finally gets released at the trans side in the form of a secretory vesicle. The secretory
vesicle gets released to the outside of the cell only on receiving stimuli.

Thus the RER and Golgi are involved in the production and release of
proteins.

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