Which organelle is responsible for synthesizing proteins and lipids?

The Endoplasmic Reticulum (ER) is indeed the organelle responsible for synthesizing proteins and lipids. It has two forms: rough ER and smooth ER. The rough ER is studded with ribosomes on its cytoplasmic surface, making it the site for protein synthesis. These ribosomes translate messenger RNA (mRNA) into polypeptide chains, which then enter the rough ER lumen for modification and folding.

Additionally, the smooth ER does not have ribosomes and is primarily involved in synthesizing lipids, detoxifying harmful metabolic byproducts, and storing calcium ions. Together, both forms of the ER play a crucial role in the synthesis and processing of biomolecules necessary for various cellular functions.

In contrast, the Golgi apparatus functions primarily in modifying, sorting, and packaging proteins and lipids produced in the ER for delivery to their destinations, rather than synthesizing them. Vesicles serve as transport vehicles for delivering materials within the cell but do not synthesize organic compounds. Lysosomes contain digestive enzymes for breaking down waste materials and cellular debris, rather than being involved in the synthesis of proteins or lipids.