Structural mimicry of puromycin:

• Puromycin does not mimic alanyl-tRNA.
• Puromycin lacks imidazole functionality and does not resemble histidyl-tRNA.
• Puromycin is a structural analog of the $3'$ terminal adenosine of tyrosyl-tRNA (tyrosinyl-tRNA); it enters the ribosomal A site and accepts the nascent polypeptide, forming peptidyl-puromycin that causes premature termination of translation.
• Prolyl-tRNA has an imino acid structure and does not resemble puromycin.

Evaluation of post-translational modifications (PTMs):

• Statement (A) is true: Proteolytic cleavage of polyprotein precursors into individual active proteins (e.g., viral polyproteins, insulin precursor) is a major PTM.
• Statement (B) is true: Post-translational hydroxylation of proline and lysine residues by prolyl and lysyl hydroxylases is essential for collagen stability.
• Statement (C) is false: In prokaryotes, formylation of methionine occurs before translation begins on the loaded initiator tRNA ($f\text{Met-tRNA}^{\text{fMet}}$); hence it is a pre-translational event.
• Statement (D) is true: Disulfide bridge formation between cysteine residues occurs post-translationally in the endoplasmic reticulum.

Ribosomal vs Non-ribosomal peptide synthesis:

• Oxytocin is encoded by the OXT gene and translated ribosomally as a preprohormone.
• Gramicidin S is a cyclic decapeptide antibiotic synthesized independently of ribosomes and mRNA templates by multienzyme non-ribosomal peptide synthetases (NRPS).
• Insulin is gene-encoded and synthesized ribosomally on the rough endoplasmic reticulum as preproinsulin.
• Actinomycin D contains non-protein amino acids and is assembled non-ribosomally by NRPS complexes in Streptomyces.