Why Smooth ER Not involved in the synthesis of proteins

Which of the following is NOT involved in

the synthesis of proteins?

(a) rough ER

(b) smooth ER

(c) Golgi body

(d) ribosomes 

Answer: (b) smooth ER.

Rough ER is the site for protein synthesis and has ribosomes embedded. Ribosomes on the rough ER

produce proteins that are passed from the cell; the Golgi body then packages them for this purpose. 

Smooth ER is used mainly in the making of lipids and detoxifying enzymes.