Lecture 11 Summary

ATP synthesis in chloroplasts is in principle the same as in mitochondria. ATP synthases are highly homologous. Differences lie in the relative contributions of DpH and DV to proton-motive force, and arise from the specific topologies of the two organelles.

The chloroplast ATP synthase is often referred to as the CFo-CF1 ATP synthase. One notable difference is the presence of 12 c-subunits in the c ring of the CFo component of this complex. This means that 12 H⁺ are translocated per 360° rotation of the c-ring, which in turn drives the generation of 3 ATP in the F1 assembly. Therefore, in chloroplasts it takes 4 H⁺ to flow back down the electrochemical gradient per ATP molecule synthesized.

Study questions

• Estimate a P:2e^– ratio for oxigenic photosynthesis, assuming each electron pair is tranferred from H₂O through both photosystems.

Page updated 01-03-07

References

1. Kramer DM, Cruz JA, Kanazawa A. (2003). Trends Plant Sci 8: 27-32.
2. Kurisu G, Zhang H, Smith JL, Cramer WA. (2003) "Structure of the Cytochrome b6f Complex of Oxygenic Photosynthesis: Tuning the Cavity". Science 302: 1009-1014.