What is the size of a eukaryotic ribosome?

A eukaryotic ribosome is classified as 80S. This designation refers to its size, which is determined by the Svedberg unit (S), a measure of the rate of sedimentation during centrifugation rather than just mass. Eukaryotic ribosomes are composed of two subunits: the large subunit, which is 60S, and the small subunit, which is 40S. Together, these subunits combine to form the functional ribosome, thus giving it an overall size of 80S.

In contrast, prokaryotic ribosomes are 70S, made up of a 50S large subunit and a 30S small subunit. Some of the other choices, like 60S and 50S, refer to the size of just one of the subunits and not the complete eukaryotic ribosome. Therefore, the understanding that the entire eukaryotic ribosome measures 80S is crucial for distinguishing it from prokaryotic ribosomes and appreciating the differences between the two domains of life.