The endoplasmic reticulum is a network of membranes found throughout the cell and connected to the nucleus. Rough ER (RER) is involved in protein production, protein folding, quality control and despatch. It is called ‘rough’ because it is studded with ribosomes.
Smooth ER (SER) is associated with the production and metabolism of fats and steroid hormones. It is ‘smooth’ because it is not studded with the ribosomes and is associated with smooth slippery fats.
The SER helps in the manufacture of fat molecules or lipids important for cell function.