Ribosomal RNA

Ribosomal RNA is essential for protein synthesis. In fact, RNA is thought to be the catalytically active part of the very large complex of proteins and RNAs that synthesize proteins. Ribosomes and ribosomal RNAs are heterogeneous, with different sized rRNAs found in the small and large subunits of the ribosome. Ribosomes can be separated into two subunits. Each subunit contains both protein and RNA. Although they vary widely in size, ribosomal RNAs have common secondary structures. The larger size of the eukaryotic RNAs is due to their having extra structural domains inserted into the midst of the smaller ones, rather than by a totally new folding pattern.

Antibiotics are natural products, usually from soil bacteria and molds, which interfere with the growth of other bacteria. Often these antibiotics act on ribosomal RNA targets. For example, streptomycin, which has been used to treat tuberculosis, binds to a single region of bacterial 16S RNA, interfering with protein synthesis. The drug doesn't disrupt protein synthesis in humans, which allows for streptomycin's relatively high therapeutic index—the ratio of harmful to helpful doses of the drug. Conversely, bacteria can become resistant to antibiotics by changes in their rRNA, either by a change in the nucleotide sequence of the ribosomal RNA or by methylation of the rRNA.