Calvin cycle
Three CO₂ in, one G3P out. Light-independent does not mean dark.
Per 3 CO₂: 1 G3P exported · costs 9 ATP + 6 NADPH
This mnemonic, unpacked word by word →
Three turns fix three CO₂ and export a single G3P; six turns make a glucose, for 18 ATP and 12 NADPH. It runs in daylight: several of its enzymes are switched on by light, so "dark reactions" is a name to unlearn. The product is G3P (students often expect glucose here).
The most abundant enzyme on Earth and one of the slowest, near 3 reactions per second. The abundance is compensation. Carboxylation makes an unstable 6-carbon intermediate that splits instantly into two 3-PGA. Rubisco also grabs O₂ by mistake (photorespiration), the wasteful habit C₄ and CAM plants evolved to dodge.
Glycolysis step 7 run backwards, paid for with light-reaction ATP. The intermediate names are the same; the direction runs the other way.
The reduction phase, using NADPH where glycolysis’s twin enzyme uses NADH. One of the six G3P leaves the cycle for sucrose and starch; the other five stay.
A carbon shuffle through the same transketolase and aldolase chemistry as the nonoxidative pentose phosphate pathway, capped by phosphoribulokinase. Count carbons: 15 in, 15 out. If the lights go off, RuBP falls and 3-PGA piles up, the classic pulse-chase graph.