Which organelle is responsible for synthesizing proteins and lipids?

The organelle responsible for synthesizing proteins and lipids is the endoplasmic reticulum (ER). This organelle comes in two forms: rough ER and smooth ER. The rough ER is studded with ribosomes on its cytoplasmic surface, which is where protein synthesis occurs. The ribosomes translate mRNA into polypeptide chains, which then enter the rough ER for folding and modification.

On the other hand, the smooth ER is involved in the synthesis of lipids, including phospholipids and steroids, and plays a key role in metabolizing carbohydrates and detoxifying certain chemicals. By integrating protein and lipid synthesis, the endoplasmic reticulum serves as a critical hub in the cell's overall function regarding the production of these essential biomolecules.

The other organelles mentioned fulfill different roles: the Golgi apparatus processes and packages proteins and lipids but does not synthesize them; vesicles transport materials within the cell; and lysosomes are involved in digestion and waste disposal, breaking down macromolecules. Thus, the endoplasmic reticulum accurately represents the organelle primarily responsible for the synthesis of both proteins and lipids.