Ribosomes are mainly made inside the nucleolus, a large spherical structure located in the nucleus of the cell. The nucleolus is known as a ribosome production factory. Its primary function is synthesizing and assembling the cell’s ribosomes. On entering the nucleus, the proteins of ribosomes bind to four rRNA strands, creating two ribosomal subunits of different sizes. Together, these make up the complete ribosome organelle.