Light reactions of photosynthesis template

PSII (P680) with water splitting, plastoquinone, cytochrome b₆f (Q cycle), plastocyanin, PSI (P700), ferredoxin and FNR making NADPH; protons pumped into the lumen drive CF₀CF₁ ATP synthase. Plastoquinone/plastoquinol structures.

What the template shows

• Linear electron flow from water to NADP⁺ through two photosystems, coupled to ATP synthesis in the thylakoid
• Thylakoid membrane: the Z scheme laid flat
• Proton numbers per O₂ released (4 e⁻)
• Stroma · low [H⁺]
• thylakoid membrane
• NADP⁺ reductase
• ATP synthase
• ADP + Pᵢ → ATP
• Mn₄CaO₅ cluster
• NADP⁺ + H⁺ → NADPH
• Thylakoid lumen · high [H⁺]
• Plastoquinone is reduced at PSII and oxidised at cytochrome b₆f
• R = isoprenoid tail (9 isoprene units, PQ-9)
• plastoquinol (PQH₂)
• Electron path: H₂O → PSII → PQ → cyt b₆f → plastocyanin (PC) → PSI → ferredoxin (Fd) → FNR → NADPH.
• Per O₂: 2 H₂O split by the Mn₄CaO₅ cluster, 8 photons (4 at each photosystem), 2 NADPH, ≈ 12 H⁺ into the lumen and ≈ 3 ATP.
• Cyclic flow around PSI (Fd → cyt b₆f → PC) makes ATP but no NADPH, adjusting the ATP : NADPH ratio.
• The ATP and NADPH made here drive the Calvin cycle in the stroma.

Drawn with 22 atoms, 1 arrow, 69 shapes – every one editable in MolDraw.

Sources

• Nelson & Cox, Lehninger Principles of Biochemistry, 8th ed., 2021 Textbook
• Berg, Tymoczko, Gatto & Stryer, Biochemistry, 9th ed., 2019 Textbook
• Voet & Voet, Biochemistry, 4th ed., Wiley 2011 Textbook