Ribosomes are cellular structures responsible for protein synthesis. They translate messenger RNA (mRNA) sequences into polypeptide chains by linking amino acids together in the order specified by the mRNA. Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, contributing to both free and membrane-bound protein production. Overall, they play a critical role in translating genetic information into functional proteins essential for various cellular processes.