Microbiology Practice Exam

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What is the total number of ribosomal subunits in eukaryotic cells?

The correct answer is: 80

In eukaryotic cells, ribosomes are composed of two subunits: the large subunit and the small subunit. The large subunit has a sedimentation coefficient of 60S, while the small subunit has a sedimentation coefficient of 40S. When combined, the sedimentation coefficients of the two subunits give a total of 80S for the entire ribosomal structure. The "S" value (Svedberg unit) indicates the size of the particles, which is not additive in a simple way due to the complex relationship between mass, shape, and sedimentation behavior. This is why, despite the subunits being 60S and 40S individually, the assembled ribosome is classified as 80S. This understanding is fundamental in microbiology and cell biology, as it highlights the complexity of ribosomal architecture and the importance of these structures in protein synthesis within eukaryotic cells.