Ribosomes are organelles composed of ribosomal proteins (riboproteins) and Ribonucleic acids (ribonucleoproteins). Created by the nucleolus, Ribosomes are bound by a membrane but are not membranous. Ribosomes are found in both eukaryotic and prokaryotic cells, ribosomes found in prokaryotic cells are generally smaller than those found in eukaryotic cells. Ribosomes main function is to create proteins, which are then carried around the cell by the ER.