From SER or RER

Just a thought to clarify

This post is made in response to a question I posted to L 2 weeks back when I asked if all polypeptide made on in the lumun of RER will pass through RER or SER or both. I highlighted that most will pass through via the SER.

I would like to clarify that there are two polypeptides that we can considered here:
1) those that are meant to be secreted out of the cell (thus exists in its entirety in the lumen)
2) proteins embedded in the membranes e.g transmembrane proteins.

In the case of 1, polypeptides formed may bud off from SER
In the case of 2, the transmembrane proteins are already embedded in the membrane of RER when they are synthesized so it make more sense to bud off directly from there