This page discusses ribosomes, crucial cellular structures responsible for protein synthesis by translating mRNA into polypeptides. Measuring about 20 nm, they exist as free entities or in clusters (p...This page discusses ribosomes, crucial cellular structures responsible for protein synthesis by translating mRNA into polypeptides. Measuring about 20 nm, they exist as free entities or in clusters (polysomes) in eukaryotes, often attached to the endoplasmic reticulum. Mitochondria possess unique ribosomes for specific protein synthesis. Although there are structural differences among ribosomes in bacteria, eukaryotes, and mitochondria, their core functions remain consistent across these types.