= Glycolysis
{tag=Energy metabolism}
{wiki}
<Glycolysis> converts one <glucose> into two <pyruvates>, yielding two net <ATP> and reducing two <NAD+> to two <NADH> in the canonical pathway. It first spends two <ATP>, then produces four by <substrate-level phosphorylation>. The pathway itself consumes no molecular <oxygen>; sustained operation nevertheless requires regeneration of <NAD+>.<Biology 2e by Mary Ann Clark and others>[§7.2, First Half of Glycolysis, step 5; Second Half of Glycolysis, steps 6–10; Outcomes of Glycolysis]{ref}
The useful organizing idea is three separate ledgers: <carbon> <chemical atoms>, transfers between <ADP> and <ATP>, and <redox> transfers between <NAD+> and <NADH>. Splitting the <carbon> skeleton doubles the number of downstream conversions; recycling a <cofactor (biochemistry)> permits repeated operation. These counts explain the yield without memorizing a drawing of every <enzyme>. The two net <ATP> belong to <glycolysis> alone, not to complete <cellular respiration>.
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