Antimetabolites mimic naturally occurring substances. Which nucleic acid building blocks do they mimic?

• A. Purine and pyrimidine
• B. Amino acids
• C. Fatty acids
• D. Nucleotides only

Answer: (A)

Antimetabolites work by imitating the actual building blocks of nucleic acids. The DNA and RNA bases come in two families: purines and pyrimidines. These drugs resemble those bases closely enough to be taken up and processed like the real substrates, becoming active forms that can be incorporated into DNA or RNA or that block enzymes needed to make nucleotides. This disruption of nucleotide synthesis and incorporation halts DNA replication and transcription, which is why they’re designed to mimic purines and pyrimidines. They do not mimic amino acids or fatty acids, and their action isn’t limited to just nucleotides, so focusing on purine and pyrimidine analogs captures the essential idea.