Which cellular structure is involved in protein synthesis?

Ribosomes are the primary cellular structures responsible for protein synthesis. These small, complex assemblies are found either floating freely in the cytoplasm or attached to the endoplasmic reticulum, creating what is known as the rough ER. During protein synthesis, ribosomes translate messenger RNA (mRNA) sequences into polypeptide chains, which then fold into functional proteins. This process involves the coordination of transfer RNA (tRNA) molecules that bring specific amino acids to the ribosome, where they are linked together in the order specified by the mRNA sequence.

Other structures such as the nucleus are important for the transcription phase of gene expression, where DNA is converted into mRNA, but they do not directly participate in the actual synthesis of proteins. Lysosomes are involved in digestion and recycling of cellular waste but have no role in protein synthesis. Vesicles transport molecules within the cell and to different destinations but do not synthesize proteins themselves. Therefore, ribosomes stand out as the key players in the process of translating genetic information into functional proteins.