Elongation of the acyl group to make fatty acids longer than 16 carbons (palmitate) occurs apart from palmitate synthesis. Whereas palmitate synthesis occurs in the cytosol, elongation occurs in both the mitochondria and endoplasmic reticulum (ER). The ER is the dominant system. Elongation in the ER differs from cytosolic synthesis in employing coenzyme A (instead of acyl carrier protein) and separate enzymes (instead of a complex). The condensation reaction occurs between malonyl-CoA and an acyl-CoA to form a -ketoacyl-CoA (see here and here). Two enzymes catalyze this step in the endoplasmic reticulum, one of which is specific for unsaturated fatty acyl-CoAs.