Puromycin is a structural analog of tyrosyl-tRNA (Option B). This antibiotic mimics the 3′ end of charged tRNA, specifically resembling tyrosyl-tRNA due to its tyrosine-like moiety linked to a modified adenosine, allowing it to bind the ribosomal A site and cause premature chain termination during translation.​

Option Analysis

• (A) Alanyl-tRNA: Incorrect. While some studies compare puromycin to alanyl-oligonucleotides in EF-Tu interactions, its core structure features a tyrosine mimic, not alanine.​

• (B) Tyrosyl-tRNA: Correct. Puromycin’s structure includes a modified tyrosine attached to the 3′ adenosine of tRNA, enabling peptidyl transfer and release of puromycylated peptides.​​

• (C) Methionyl-tRNA: Incorrect. Methionyl-tRNA initiates translation at the P site; puromycin targets the A site like elongator tRNAs, not the initiator.​

• (D) Glycyl-tRNA: Incorrect. Glycine lacks the aromatic ring in puromycin’s amino acid analog, which matches tyrosine’s structure.​

Puromycin, a key topic in CSIR NET Life Sciences, acts as a puromycin structural analog tyrosyl-tRNA, disrupting translation by mimicking the 3′ end of aminoacyl-tRNA. This antibiotic, produced by Streptomyces alboniger, enters the ribosomal A site, accepts the nascent peptide via peptidyl transferase, and releases truncated puromycylated chains, halting elongation.​

Mechanism in Translation

Puromycin binds the A site like elongator tyrosyl-tRNA, featuring an amide-linked tyrosine mimic instead of an ester bond. The ribosome transfers the P-site peptide to puromycin, preventing further amino acid addition due to its non-extendable structure. This makes it a tool for studying ribosome function and selecting transfected cells.​

Exam Relevance for CSIR NET

In competitive exams, questions test puromycin’s mimicry of tyrosyl-tRNA over alanyl, methionyl, or glycyl-tRNA. Focus on its A-site binding and premature termination for scoring in molecular biology units.​