What are the ribosomes composed of?

Ribosomes are composed of two subunits, a large and a small subunit. The small and large subunits of eukaryotes are 40S and 60s respectively. Prokaryotes consist of small 30S and large 50S subunits. Both eukaryotic and prokaryotic ribosome subunits consist of a fluctuating number of ribosomal proteins and ribosomal RNA (rRNA). Ribosomes have one binding site for mRNA, and three binding sites for transfer RNA (tRNA) molecules. In prokaryotes, ribosomes are about 40% protein and 60% rRNA. In eukaryotes, ribosomes are made up of 50% protein and 50% rRNA. Ribosomes typically are made up of 3 or 4 rRNA molecules, and about 40 to 80 different ribosomal proteins.