Peptidyl secondary structure

Ribosomal Protein Synthesis Inhibitors. Figure 5 Nucleotides at the binding sites of chloramphenicol, erythromycin and clindamycin at the peptidyl transferase center. The nucleotides that are within 4.4 A of the antibiotics chloramphenicol, erythromycin and clindamycin in 50S-antibiotic complexes are indicated with the letters C, E, and L, respectively, on the secondary structure of the peptidyl transferase loop region of 23S rRNA (the sequence shown is that of E. coll). The sites of drug resistance in one or more peptidyl transferase antibiotics due to base changes (solid circles) and lack of modification (solid square) are indicated. Nucleotides that display altered chemical reactivity in the presence of one or more peptidyl transferase antibiotics are boxed. 

The RNA world hypothesis proposes that RNA-based living systems predated current DNA-based life. Individual RNAs, which can store information like DNA and furthermore catalyze reactions virtually like protein enzymes, may have supported cellular and/or precellular life. The naturally occurring catalytic RNA molecules are highly specific such as the small subunit bacterial ribosomal RNA that is active as a RNA peptidyl transferase. In general, ribozymes seem to be relics from the RNA world. Many different synthetic ribozymes produced in the laboratory have diverse but defined specificities. The specificity of ribozymes is due to the intrinsic chiral centers of the RNA molecules of secondary and tertiary structure. The main evidence for an RNA world is the three essential RNA classes that act in concert to direct the specific and successive biosynthesis of proteins tRNA, rRNA, and mRNA. 

---