Final answer:
The E. Coli 70S ribosome consists of a 30S small subunit and a 50S large subunit; these labels indicate their respective sedimentation coefficients and are critical for the ribosome's protein synthesis function.
Step-by-step explanation:
The E. Coli 70S ribosome is comprised of two distinct subunits, each of different sizes. The small subunit is described as 30S, housing the 16S rRNA, and the large subunit is coined as 50S, which includes the 5S and 23S rRNA subunits. Notably, these Svedberg units are not additive, meaning that despite the subunits being labeled 30S and 50S, when combined, they maintain a total sedimentation coefficient of 70S, characteristic of the entire prokaryotic ribosome. This ribosomal structure is vital for protein synthesis, dissociating into its subunits when not actively translating mRNA, and then reassociating during the initiation of translation.