What is thethe protein-assembly factories of the cell, are present in prokaryotic cells, animal cells, and plant cells.

The assembly factories would be the endoplasmic reticulum (ER). There is two types a rough ER which has ribosomes through out its folds that do protien production, folding and quality control. The second ER is Smooth ER and it lacks ribpsomes this one is associated with the production and metabolism of fats and steroid hormones.