Abstract: Every cell in the biosphere must carry out up to billions of reactions per second. Consequently, cells are challenged to regulate the synthesis, transport, and/or trafficking of an unfathomable number of metabolites, many of which are highly reactive. How do cells and organisms ensure the correct substrates end up in the right location, at the right time, and with the right protein, while mitigating deleterious side reactions that can kill the organism? Research in the Reddi lab is focused on how cells generate and/or assimilate two key types of reactive metabolites – transition metals and reactive oxygen species. In this talk, I will present two vignettes that highlight the Reddi lab’s progress over the last ten years in developing chemical and biochemical tools that can be integrated with molecular genetics and cell biological approaches to probe heme-iron and hydrogen peroxide metabolism, two essential metabolites essential for life in air.