Ribosome catalysis — On which ribosomal subunit does the peptidyl transferase reaction (peptide bond formation) occur?

Introduction:
Peptidyl transferase is the central catalytic step of translation, forming peptide bonds between amino acids carried by tRNAs. Knowing where this reaction occurs clarifies ribosome function and the RNA world concept of ribozymes.

Given Data / Assumptions:

• Bacterial ribosome: 50S large + 30S small subunits; eukaryotic: 60S + 40S.
• The peptidyl transferase center (PTC) is rRNA-based (23S in bacteria, 28S in eukaryotes).
• tRNAs occupy A, P, E sites spanning the large subunit platform.

Concept / Approach:
Assign catalysis to the correct subunit: peptide bond formation is an rRNA-catalyzed reaction in the large subunit, not the small subunit (which primarily handles decoding and mRNA/tRNA alignment).

Step-by-Step Solution:

Verification / Alternative check:
High-resolution structures and biochemical assays (e.g., protein-free 50S showing peptidyl transferase activity) confirm rRNA (not protein enzymes) catalyzes the reaction in the large subunit.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming proteins of the large subunit catalyze the reaction; in fact, rRNA is the main catalyst.

Final Answer:
On the large ribosomal subunit.