= Glycolysis carbon and ATP ledger
{c}
Follow one <glucose> through canonical <glycolysis>, with no diversion of intermediates into other <metabolic pathways>. The investment stage uses two <ATP> to prepare the six-<carbon> <substrate>. Cleavage and rearrangement provide two <glyceraldehyde 3-phosphate> <molecules>, each containing three <carbon> <chemical atoms>. Each then yields one three-<carbon> <pyruvate>, one <NADH>, and two <ATP> in the payoff stage.<Biology 2e by Mary Ann Clark and others>[§7.2, steps 3–7 and 10; Figures 7.8–7.9 captions: investment, two glyceraldehyde 3-phosphate molecules and duplicated payoff]{ref}
\Image[/glycolysis-carbon-atp-stages.png]
{title=<Glycolysis> preserves six <carbon> <chemical atoms> while four gross <ATP> repay a two-<ATP> investment}
{description=Original aggregate-stage schematic per <glucose>, not a complete <enzyme> map or measured data. Dots count <carbon> <chemical atoms>, without assigning their positions in the <molecules>. Both three-<carbon> routes perform the same payoff sequence. The running <ATP> ledger starts at zero relative to the initial inventory; negative two means expenditure from an existing pool.}
The material check is $6=2\times3$: all six <carbon> <chemical atoms> remain in the two <pyruvates>. No <carbon dioxide> has been released within this boundary. In the <ATP> ledger, each three-<carbon> route contains two <ATP>-forming transfers, so
$$
\text{gross ATP}=2\times2=4,\qquad
\text{net ATP}=4-2=2.
$$
The first pair of payoff transfers only restores the initial <ATP> inventory; the second pair creates the net gain. Four newly formed <ATP> is therefore compatible with only two additional <ATP> remaining.
For an original scaled example, stipulate complete conversion of $5\,\mathrm{\mu mol}$ of <glucose>. The initial $30\,\mathrm{\mu mol}$ of <carbon> <chemical atoms> becomes $10\,\mathrm{\mu mol}$ of <pyruvate>, still containing $30\,\mathrm{\mu mol}$ of <carbon> <chemical atoms>. The pathway spends $10\,\mathrm{\mu mol}$ of <ATP>, forms $20\,\mathrm{\mu mol}$ of <ATP>, and adds $10\,\mathrm{\mu mol}$ to the <ATP> inventory before any other <ATP> use. It also reduces $10\,\mathrm{\mu mol}$ of <NAD+>. These are calculated ideal amounts, not observed yields; side routes or incomplete conversion change the outcome.
A common biochemical net <chemical equation> is
$$
\begin{aligned}
\mathrm{glucose}+2\,\mathrm{ADP}+2\,\mathrm P_i+2\,\mathrm{NAD}^{+}
\longrightarrow {}&2\,\mathrm{pyruvate}+2\,\mathrm{ATP}\\
&+2\,\mathrm{NADH}+2\,\mathrm H^{+}+2\,\mathrm{H_2O}.
\end{aligned}
$$
Here $\mathrm P_i$ is <inorganic phosphate>. The names group biochemical <protonation> and metal-binding states; the displayed <proton> and <water> terms use a common shorthand rather than a unique specification of every <chemical species>. The robust ledger records two net <ADP>-to-<ATP> conversions and two <NAD+>-to-<NADH> conversions. Summing the individual <chemical equations> cancels two invested <ATP> against four formed <ATP> and cancels the internal <substrates>, giving those coefficients.
Back to article page
