Practice question

Chemical sequencing with hydrazine exploits differential reactivity of pyrimidines. Hydrazine opens pyrimidine rings, rendering them susceptible to piperidine-mediated backbone scission. The reaction outcome depends on salt concentration. Hydrazine without added sodium chloride modifies both thymine and cytosine, yielding a combined T plus C cleavage lane. Adding high salt such as NaCl or using prolonged conditions suppresses thymine reaction, leaving cytosine-specific cleavage. Comparison of two lanes allows distinction between T and C. Purines A and G remain unreactive to hydrazine; they require other chemicals.