Mnemonics
Cytosol

Pentose phosphate pathway

Reducing power and ribose, with no ATP made.

Per G6P: 2 NADPH · 1 CO₂ · 1 ribulose-5-phosphate

The point
NADPH is for Production; NADH is for Power
The thiamine (B1) enzymes
ATP: Alpha-ketoglutarate dehydrogenase, Transketolase, Pyruvate dehydrogenase

This mnemonic, unpacked word by word →

The oxidative phase is irreversible. NADPH is for reductive biosynthesis and antioxidant defense, and takes no part in making ATP.

1
Glucose-6-phosphate 6-Phosphogluconate
Glucose-6-phosphate dehydrogenaserate-limiting NADP⁺ → NADPH

Rate-limiting. Activated by NADP⁺, inhibited by NADPH. Pure supply and demand on reducing power. Strictly the product is 6-phosphogluconolactone, hydrolyzed by a lactonase. Deficiency causes hemolytic anemia under oxidative stress.

2
6-Phosphogluconate Ribulose-5-phosphate
6-Phosphogluconate dehydrogenase NADPH + CO₂

The CO₂ released here is C-1 of the original glucose, which is the basis of the classic radiolabel experiment.

3
Ribulose-5-phosphate Ribose-5-phosphate
Phosphopentose isomerase

Ribose-5-phosphate feeds nucleotide synthesis. End of the oxidative phase.

4
Ribose-5-P + Xylulose-5-P Sedoheptulose-7-P + G3P
Transketolase

Non-oxidative phase, reversible carbon shuffling. Requires thiamine (B1) as TPP. 5C + 5C → 7C + 3C.

5
Sedoheptulose-7-P + G3P Erythrose-4-P + F6P
Transaldolase

7C + 3C → 6C + 4C. Every carbon is conserved and rearranged. Count the carbons and both sides total ten.