Why are proteins always made in N to C direction?​?

Question

Why are proteins always synthesized from the *N*-terminus to the *C*-terminus? Can there be any “reverse” peptide-bond formation to synthesize proteins in the *C*-terminal to the *N*-terminal direction?

Answer 1

The specific directionality of the bond formation is due to the enzymatic activity of peptidyl transferase, found in the ribosome and activated by the rRNA. This is the enzyme that catalyzes the addition of the tRNA amino acid to the growing polypeptide chain. The amino acids are attached to the tRNA and must form a bond with the previous amino acid as well as be released from the tRNA. The amino acid is attached to the tRNA by the carboxyl group (ester bond) leaving the amino group free.