Protein synthesis occurs in the ribosome, a cellular structure found in both prokaryotic and eukaryotic cells. Ribosomes can be found free-floating in the cytoplasm or attached to the endoplasmic reticulum. They facilitate the translation of messenger RNA (mRNA) into polypeptide chains, which later fold into functional proteins. Ribosomes play a crucial role in gene expression as they assemble amino acids in the specific order dictated by the mRNA sequence, which ultimately determines the protein’s structure and function.