Prokaryotes Vs. Eukaryotes
Both prokaryotic and eukaryotic ribosomes can be broken down into two subunits (the S in 16S represents Svedberg units), nt= length in nucleotides of the respective rRNAs, for exemplary species Escherichia coli (prokaryote) and human (eukaryote):
| Type | Size | Large subunit (rRNAs) | Small subunit (rRNA) |
| prokaryotic | 70S | 50S (5S : 120 nt, 23S : 2906 nt) | 30S (16S : 1542 nt) |
| eukaryotic | 80S | 60S (5S : 121 nt, 5.8S : 156 nt, 28S : 5070 nt) | 40S (18S : 1869 nt) |
Note that the S units of the subunits (or the rRNAs) cannot simply be added because they represent measures of sedimentation rate rather than of mass. The sedimentation rate of each subunit is affected by its shape, as well as by its mass. The nt units can be added as these represent the integer number of units in the linear rRNA polymers (for example, the total length of the human rRNA = 7216 nt).
Read more about this topic: Ribosomal RNA
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