Antibiotics Target: DNA

Question 1

Mitomycin C

Answer 1

Aziridine containing DNA alkylater
targets G/C bases on complementary strand -> G cross linking -> prevents strand separation and hence DNA replication and transcription

Question 2

Rifamycin

Answer 2

Bacteriocidal DNA dependent RNA polymerase inhibitor
Binds to allosteric site in DNA/RNA β subunit tunnel, blocking initiation of RNA synthesis
Analogous to macrolides which act at the translation level
Used to treat mycobacterium infections

Question 3

Sulfamethoxazole

Answer 3

Sulfa drug; p-aminobenzoate analogue
Competitively inhibits DHPS (DiHydroPteroate Synthase)
Prevents formation of 7,8- DiHydroPteroate, methyl carrier needed for dTMP -> DNA synthesis

Question 4

Trimethoprim

Answer 4

Inhibits DHFR (DiHydroFolate Reductase)
Prevents formation of 7,8-tetrahydrofolate, a methyl carrier coenzyme for dTMP and therefore DNA synthesis

Question 5

Co-Trimoxazole

Answer 5

Combination of TRImethoprim and sulfaOXAZOLE
Works by targeting two enzymes in the same cascade - DHFR has a specific bacterial isotype and DHPS is only present in bacteria
Withdrawn mostly in UK due to serious allergic reactions but still used in AIDS patients with fungal infections

Question 6

Ciprofloxacin

Answer 6

Fluoroquinolone broad spec antibiotic. Bacteriocidal
Targets DNA gyrase (bacterial DNA type II topoisomerase)
Second target: topoisomerase IV (-> ATP dependent DNA relaxation)
Used in UTIs, pneumonia, gastroenteritis, anthrax, pseudomonas.
Other quinolones: levofloxacin and gatifloxacin (Λgram +ve potency)