Name two classes of compounds that inhibit DNA replication or transcription, and give an example of each.

Name two classes of compounds that inhibit DNA replication or transcription, and give an example of each.

• A. Nucleoside analogs (AZT) terminate DNA synthesis; transcription inhibitors (rifampicin) block bacterial RNA polymerase.
• B. Protease inhibitors (ritonavir) terminate DNA synthesis; lipid synthesis inhibitors stop RNA translation.
• C. Amino acid analogs stop transcription; protein synthesis inhibitors terminate replication.
• D. Intercalating dyes trigger replication; metal chelators terminate transcription.

Answer: (D)

Two main categories of compounds that inhibit DNA replication or transcription are nucleoside analogs and transcription inhibitors. Nucleoside analogs resemble the normal nucleosides that make up DNA. When a polymerase encounters one, it can incorporate it into the growing DNA strand, but if the analog lacks the essential 3′-hydroxyl group, DNA synthesis cannot continue, leading to chain termination. AZT is a thymidine analog used to block viral DNA synthesis because the reverse transcriptase cannot extend past the incorporated analog. Transcription inhibitors work by directly blocking RNA synthesis. Rifampicin, for example, binds to bacterial RNA polymerase and prevents the initiation of transcription, stopping RNA production in bacteria. Other options don’t fit as cleanly: protease inhibitors target protein processing rather than DNA replication; translation and lipid synthesis aren’t the direct targets here; intercalating dyes can disrupt DNA structure and broadly affect replication and transcription but aren’t a tight, well-defined class with a specific, standard example like rifampicin; metal chelators remove essential metals and can impact many processes, not a focused mechanism of transcription inhibition.

Two main categories of compounds that inhibit DNA replication or transcription are nucleoside analogs and transcription inhibitors. Nucleoside analogs resemble the normal nucleosides that make up DNA. When a polymerase encounters one, it can incorporate it into the growing DNA strand, but if the analog lacks the essential 3′-hydroxyl group, DNA synthesis cannot continue, leading to chain termination. AZT is a thymidine analog used to block viral DNA synthesis because the reverse transcriptase cannot extend past the incorporated analog.

Transcription inhibitors work by directly blocking RNA synthesis. Rifampicin, for example, binds to bacterial RNA polymerase and prevents the initiation of transcription, stopping RNA production in bacteria.

Other options don’t fit as cleanly: protease inhibitors target protein processing rather than DNA replication; translation and lipid synthesis aren’t the direct targets here; intercalating dyes can disrupt DNA structure and broadly affect replication and transcription but aren’t a tight, well-defined class with a specific, standard example like rifampicin; metal chelators remove essential metals and can impact many processes, not a focused mechanism of transcription inhibition.