**Core Concept**
Puromycin is a naturally occurring antibiotic that structurally resembles aminoacyl t-RNA and inhibits protein synthesis in both prokaryotes and eukaryotes by a unique mechanism. This unique mechanism involves the addition of puromycin to the growing peptide chain, leading to premature chain termination and inhibition of protein synthesis.

**Why the Correct Answer is Right**
Puromycin structurally resembles aminoacyl t-RNA and is recognized by the ribosome as a legitimate amino acid, allowing it to be incorporated into the growing peptide chain. However, once incorporated, puromycin causes premature chain termination by being released from the ribosome as a completed polypeptide, thereby inhibiting protein synthesis. This mechanism of action makes puromycin effective against both prokaryotic and eukaryotic cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Azithromycin is a macrolide antibiotic that inhibits protein synthesis by binding to the 50S subunit of the bacterial ribosome, not by structurally resembling aminoacyl t-RNA.

**Option B:** Tetracycline is a broad-spectrum antibiotic that inhibits protein synthesis by binding to the 30S subunit of the bacterial ribosome, preventing the attachment of aminoacyl t-RNA to the ribosomal A site.

**Option C:** Chloramphenicol inhibits protein synthesis by binding to the 50S subunit of the bacterial ribosome, preventing peptide bond formation, not by structurally resembling aminoacyl t-RNA.

**Clinical Pearl / High-Yield Fact**
Puromycin's unique mechanism of action and broad-spectrum activity make it a valuable tool in the laboratory for studying protein synthesis and in the clinic for treating certain infections, particularly those caused by resistant bacteria.

**✓ Correct Answer: D. Puromycin**