Which organelle is involved in the synthesis of lipids and the processing of proteins?

• A. Ribosomes
• B. Lysosomes
• C. Centrioles
• D. Endoplasmic Reticulum

Answer: (D)

Think about where fats are made and where proteins are processed after they’re made. The endoplasmic reticulum is a network inside the cell that handles both tasks. The rough part of the ER is studded with ribosomes and is the site where proteins destined for secretion or membranes begin to be synthesized and undergo initial processing. The smooth part lacks ribosomes and specializes in lipid (fat) synthesis and other metabolic duties. As proteins enter the ER, they are folded and chemically modified before moving on to the Golgi apparatus for further processing. In contrast, ribosomes themselves are the sites of protein synthesis but don’t build lipids; lysosomes break down waste, and centrioles organize microtubules during cell division. So the organelle that combines lipid synthesis with protein processing is the endoplasmic reticulum.