The structures in cells responsible for protein synthesis are called ribosomes. Ribosomes can be found either floating freely in the cytoplasm or attached to the endoplasmic reticulum, forming the rough ER. They translate messenger RNA (mRNA) into polypeptide chains, assembling individual amino acids into proteins according to genetic instructions. This process is critical for cell function and regulation, as proteins perform various roles, including structural support, enzymatic activity, and signaling. Ribosomes are vital components in the central dogma of molecular biology.