Which is a tiny structure located in the cytoplasm of a cell?

A ribosome is a tiny structure located in the cytoplasm of a cell, where it builds proteins.

Ribosomes read genetic instructions carried by messenger RNA and join amino acids in the specified order, creating polypeptide chains that fold into proteins. They are made of ribosomal RNA and proteins and consist of a small subunit plus a large subunit. Ribosomes may float freely in the cytoplasm or attach to the rough endoplasmic reticulum when making proteins destined for secretion or membranes.

The structure was first observed in the 1950s by cell biologist George Emil Palade, whose electron-microscope images revealed dense particles initially nicknamed “Palade granules.” The word ribosome was introduced in 1958. Ribosomes occur in every type of cell, including bacteria, although bacterial ribosomes are smaller than those in the cytosol of eukaryotic cells.

A common mix-up is calling a ribosome a membrane-bound organelle: it is often grouped with cell structures, but it has no surrounding lipid membrane. Another nearby fact is that ribosomes are assembled partly in the nucleolus of eukaryotic cells before their subunits are exported to the cytoplasm.