In endoplasmic reticulum the reactions resemble those of de novo fatty acid synthesis.
The overall reaction:
This shows the overall process of fatty acyl elongation in the endoplasmic reticulum. The process resembles that catalyzed by fatty acyl synthase, but the individual activities appear to be on separate enzymes.
Notice that malonyl CoA is the source of the added carbons, as in de novo fatty acid synthesis.
The activities are closely associated with the endoplasmic reticulum membranes.
The activities are separable; they are not part of a multifunctional enzyme.
No ACP is involved; CoA esters are used directly.