= Deoxyadenosine triphosphate
{title2=$\mathrm{dATP}$}
<Deoxyadenosine triphosphate>, usually abbreviated dATP, is a <nucleotide> containing <adenine>, a <deoxyribose> sugar and three phosphate groups. The “deoxy” distinguishes its sugar from the ribose in <adenosine triphosphate>. The usual molecular formula for the neutral acid is $\mathrm{C_{10}H_{16}N_5O_{12}P_3}$; its ionization state in solution depends on conditions.<Deoxyadenosine triphosphate in PubChem>[CID 15993, identity and molecular formula]{ref}
A <DNA polymerase> uses dATP as the substrate for adding an adenine-containing unit to a growing <DNA> strand opposite a template <thymine>. The strand's terminal $3'$ hydroxyl attacks the incoming nucleotide's alpha phosphate; the other two phosphates leave as <pyrophosphate>. The incorporated unit is therefore a monophosphate residue within the chain, not a triphosphate hanging from the completed backbone. This distinction connects nucleotide chemistry with the directional $5'\to3'$ growth of <DNA>.https://www.ncbi.nlm.nih.gov/books/NBK26850/[Molecular Biology of the Cell, DNA Replication Mechanisms, incoming deoxyribonucleoside triphosphates and the growing 3-prime end]{ref}
A polymerase assay can supply the template, primer, enzyme and nucleotide substrates, then compare product lengths with and without dATP. A failure to extend past a template position requiring adenine tests substrate dependence; it does not by itself determine every enzymatic step.
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