Practice question

5-bromouracil is synthetic halogenated pyrimidine analog structurally similar to thymine where bromine atom replaces methyl group at C5 position, preserving Watson-Crick face that pairs with adenine in keto form. Size and electronegativity allow efficient incorporation by DNA polymerases opposite adenine during S-phase when thymine is substituted. Once embedded, bromine increases tendency to tautomerize to enol form that pairs with guanine, providing mutagenic potential exploited historically for inducing directed transitions in bacteriophage and bacterial genetics. This principle illustrates essential molecular mechanisms governing replication fidelity and mutation fixation relevant for exam interpretation.