When is agranular ER attached to granular ER?

Question

When is agranular ER attached to granular ER?

Answer 1

Granular ER = rough ER = the ER that is involved in making membrane and secreted proteins.  

Agranular ER = smooth ER = the ER that is involved in making lipids and steroids.

Essentially, every eukaryotic cell has rough ER = they all need to make membrane proteins.  Probably every cell also has smooth ER = they all need to make membrane lipids.  And, as far as I know, they are attached to each other every time:  the ER is an extension of the nuclear membrane, and both the SER and RER are continuous with the nuclear membrane and with each other.

So:  the granular RER is always attached to the agranular SER.  Different cells have different needs and capacities for making membrane/secreted proteins and lipids/steroids so the proportions differ, but they are always both present and connected.

Hope this helps.