Is rRNA a ribozyme?

• A. Yes
• B. No
• C. Sometimes
• D. Only in eukaryotes

Answer: (A)

RNA can act as a catalyst, and rRNA within the ribosome is the catalytic core that drives peptide bond formation. In both bacteria and eukaryotes, the large subunit’s rRNA forms the peptidyl transferase center, where the chemistry of joining amino acids happens. The active site is built by rRNA nucleotides that precisely orient the substrates and stabilize the transition state, meaning the RNA itself does the catalysis. Ribosomal proteins, while essential for structure and efficiency, mainly support the ribosome’s shape and assembly rather than perform the chemical step. This is a classic example of a ribozyme: the RNA component has the catalytic power, not the proteins. In bacteria the key catalytic RNA is the 23S rRNA (with 5S also present), and in eukaryotes it’s the 28S rRNA, underscoring that the RNA-based catalysis is conserved across life.