Q.40. Polypeptides are either biosynthesized on the ribosomes using an mRNA template or chemically
synthesized by the Merrifield’s solid phase method. The correct directions of peptide synthesis are
(A) C → N direction on the ribosomes and N → C direction on the solid phase
(B) N → C direction on the ribosomes and C → N direction on the solid phase
(C) N → C direction in both cases
(D) C → N direction in both cases

Polypeptides form through ribosomal biosynthesis using mRNA or chemical synthesis via Merrifield’s solid-phase method, differing in directionality. The correct answer is option (A): C → N direction on ribosomes and N → C on solid phase.​

Correct Answer

Option (A) states C → N direction on ribosomes and N → C on solid phase, which matches biological and chemical processes.​

Ribosomes read mRNA from 5′ to 3′, starting with initiator tRNA at the N-terminus (amino end); new amino acids add to the C-terminus (carboxyl end), so synthesis proceeds N → C.​

In Merrifield’s solid-phase synthesis, the C-terminal amino acid attaches first to resin; protected N-terminal amino acids couple sequentially toward the N-end, yielding C → N growth.​

Option Explanations

• (A) Correct: Matches ribosomal N → C and solid-phase C → N directions.​

• (B) Incorrect: Reverses both; ribosomes synthesize N → C, not C → N.​

• (C) Incorrect: Solid phase uses C → N, not N → C.​

• (D) Incorrect: Ribosomes use N → C, not C → N.​