Metabolic pathway
Light reactions
Uses light to strip electrons from water and carry them, through two photosystems in series, to NADP+. Along the way it piles up protons in the thylakoid lumen, and with that gradient it makes ATP. The map follows the path of the electron: the Z-scheme.
- In
- 2 NADP+ + 3 ADP + 3 Inorganic phosphate
- Out
- Oxygen + 2 NADPH + 3 ATP + Water + 2 Proton
- Location
- Thylakoid membrane
Fun facts
- Photosystem IIThe center that makes the cut is a cluster of four manganese atoms and one calcium atom. It stores the four positive charges one at a time and only then releases the oxygen all at once, so as not to let intermediate products loose.
- Photosystem IDrawn with energy on the vertical axis, the route is shaped like a Z: it rises with light, falls while being carried, and rises again. Hence the name Z-scheme.
- Chloroplast ATP synthaseThe thylakoid gradient is mostly one of acidity, not charge: the lumen becomes a thousand times more acidic than the stroma. In the mitochondrion the voltage difference counts for more.
Reactions
| # | Enzyme | ΔG°′ |
|---|---|---|
| 1 | Photosystem IIEC 1.10.3.9 · irreversible2 Water + 2 Plastoquinone + 4 Proton → 2 Plastoquinol + Oxygen + 4 Proton (thylakoid lumen) | — |
| 2×2 | Cytochrome b6f complexEC 7.1.1.6 · irreversiblePlastoquinol + 2 Oxidized plastocyanin + 2 Proton → 2 Reduced plastocyanin + Plastoquinone + 4 Proton (thylakoid lumen) | — |
| 3×4 | Photosystem IEC 1.97.1.12 · irreversibleReduced plastocyanin + Oxidized ferredoxin → Oxidized plastocyanin + Reduced ferredoxin | — |
| 4×2 | Ferredoxin-NADP+ reductaseEC 1.18.1.2 · irreversible2 Reduced ferredoxin + NADP+ + Proton → 2 Oxidized ferredoxin + NADPH | — |
| 5×3 | Chloroplast ATP synthaseEC 7.1.2.2ADP + Inorganic phosphate + 4 Proton (thylakoid lumen) ⇌ ATP + Water + 4 Proton | — |
0 of 5 reactions with a documented ΔG.
Use Shift to select several
The data sheet includes the map. The logo goes at the bottom.
Sources
- Nelson, D. L. & Cox, M. M. (2021). Lehninger. Principios de bioquímica, 8.ª ed., ch. 20