Ribosomes are composed of two main subunits: the large subunit and the small subunit. In eukaryotic cells, the ribosome subunits are referred to as the 60S (large) and 40S (small) subunits, while in prokaryotic cells, they are known as the 50S (large) and 30S (small) subunits.
Each ribosomal subunit is made up of ribosomal RNA (rRNA) and ribosomal proteins. The rRNA forms the core structure of the ribosome and is crucial for its function, while the proteins provide structural support and play roles in the ribosome's assembly and function during translation. In eukaryotes, for example, the 60S subunit contains three rRNA molecules (28S, 5.8S, and 5S rRNA) and around 49 different proteins, while the 40S subunit contains one rRNA molecule (18S rRNA) and about 33 proteins.
Overall, the ribosome is a complex macromolecular machine essential for protein synthesis in all living cells.