In which organelle does protein synthesis occur?

Protein synthesis primarily occurs in ribosomes, which are the cellular structures responsible for translating the genetic code from messenger RNA (mRNA) into proteins. Ribosomes can be found either floating freely in the cytoplasm or attached to the endoplasmic reticulum, forming what's known as the rough endoplasmic reticulum. The ribosome reads the sequence of the mRNA and, with the help of transfer RNA (tRNA), assembles amino acids in the correct order to form a polypeptide chain, ultimately folding into a functional protein.

Other organelles like mitochondria and chloroplasts have some roles in protein synthesis, particularly in the synthesis of proteins encoded by their own DNA, but the primary site for the synthesis of all proteins in eukaryotic cells is the ribosome. Vacuoles function mainly in storage and maintaining turgor pressure in plant cells, thus they do not directly participate in protein synthesis.