What forms the peptide bond during translation? Amino acids are covalently joined into a growing protein chain on the ribosome by which catalytic activity?

Introduction:
Protein synthesis on the ribosome involves repeatedly forming peptide bonds between amino acids. The catalytic engine responsible is part of the ribosome itself, specifically RNA-based catalysis, highlighting the ribosome’s nature as a ribozyme.

Given Data / Assumptions:

• The ribosome consists of rRNAs and proteins; the large subunit houses the peptidyl transferase center.
• tRNAs position amino acids, but catalysis is carried out by rRNA.
• Hydrogen bonds are noncovalent and cannot form peptide bonds.

Concept / Approach:

Peptide bond formation is catalyzed by the ribosomal RNA of the large subunit (23S rRNA in bacteria; 28S in eukaryotes). This peptidyl transferase activity transfers the growing polypeptide from the P-site tRNA to the amino group of the A-site aminoacyl-tRNA.

Step-by-Step Solution:

Verification / Alternative check:

Mutational and biochemical evidence shows that rRNA residues, not ribosomal proteins, form the catalytic site; experiments with protein-depleted ribosomes retain peptidyl transferase function.

Why Other Options Are Wrong:

tRNA is an adaptor, not the catalytic enzyme. DNA polymerase acts in DNA replication, not translation. Hydrogen bonds stabilize structure but do not create covalent peptide bonds. mRNA provides the template but no catalytic activity.

Common Pitfalls:

Attributing catalysis to ribosomal proteins or to tRNA rather than to rRNA.

Final Answer:

The peptidyl transferase activity of ribosomal RNA within the large subunit