The ribosome is a two-part
structure composed of protein and ribosomal RNA (rRNA). It is composed
of small and large subunits that join during the process of protein synthesis.
Ribosome size in Svedburg (S) units, a measure of the rate at which they
settle in a tube during centrifugation. Prokaryote ribosomes have
30S (small) and 50S (large) subunits that joined together have a size of
70S, while eukaryotic ribosomes are larger, having a size of 80S.
The cytoskeleton is an internal framework of protein fibers that helps compose the shape of many cells. Spherical bacteria lack cytoskeleton structure, though rod-shaped bacteria have simple one. Eukaryotic cells use the cytoskeleton to provide support, but also in the movement of large organelles (cyclosis) and in transport processes such as endocytosis. The image above shows the cytoskeleton of Bacillus subtilis. This structure is composed of a single helical protein.