1. Mitochondria and respiratory chains
SBS-922 Membrane Proteins
Mitochondria and respiratory chains
John F. Allen
School of Biological and Chemical Sciences, Queen Mary, University of London

2. The cytochrome b6f complex
The chloroplast homologue of respiratory complex III:
The cytochrome b6f complex

3. Light Light NADP+ FNR Fd Cyt b6f PS II n-side PQ p-side PS I 2H+ 2H2O
Chloroplast stroma
Light
Light
NADP+
FNR Fd
Cyt b6f
PS II
n-side PQ
p-side
PS I
2H+
2H2O
O H+
PC, Cyt c6
Chloroplast lumen

4. Crofts, A. R. (2004) The Q-cycle, - a personal perspective. Photosynth
Crofts, A. R. (2004) The Q-cycle, - a personal perspective. Photosynth. Res.

5. Crofts, A. R. (2004) The Q-cycle, - a personal perspective. Photosynth
Crofts, A. R. (2004) The Q-cycle, - a personal perspective. Photosynth. Res.

6. Crofts, A. R. (2004) The Q-cycle, - a personal perspective. Photosynth
Crofts, A. R. (2004) The Q-cycle, - a personal perspective. Photosynth. Res.

7. The Modified Q-cycle. The experiments from the Crofts lab in the early 1980’s provided severe constraints that limited the types of plausible Q-cycle model. This version is essentially the same as that proposed by Crofts et al 1982, and reviewed by Crofts (1986)
Crofts, A. R. (2004) The Q- cycle, - a personal perspective. Photosynth. Res.

18. Why do mitochondria and chloroplasts have genome?

19. Typical prokaryotic (left) and eukaryotic (right) cells.
W. Ford Doolittle Nature 392, 15-16, 1998

20. The endosymbiont hypothesis for the origin of mitochondria.
W. Ford Doolittle Nature 392, 15-16, 1998

21. Why Do Mitochondria and Chloroplasts Have Their Own Genetic Systems?
Problem
Why Do Mitochondria and Chloroplasts Have Their Own Genetic Systems?
Why do mitochondria and chloroplasts require their own separate genetic systems when other organelles that share the same cytoplasm, such as peroxisomes and lysosomes, do not? …. The reason for such a costly arrangement is not clear, and the hope that the nucleotide sequences of mitochondrial and chloroplast genomes would provide the answer has proved unfounded. We cannot think of compelling reasons why the proteins made in mitochondria and chloroplasts should be made there rather than in the cytosol.
Molecular Biology of the Cell
© 1994 Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff, Keith Roberts, and James D. Watson
Molecular Biology of the Cell, 3rd edn. Garland Publishing

22. Why Do Mitochondria and Chloroplasts Have Their Own Genetic Systems?
Proposed solutions (hypotheses)
There is no reason. “That’s just how it is”. (Anon)
The “Lock-in” hypothesis. (Bogorad, 1975). In order for core components of multisubunit complexes to be synthesised, de novo, in the correct compartment.
The evolutionary process of transfer of genes from organelle to nucleus is still incomplete.
E.g. Herrmann and Westhoff, 2001: The partite plant genome is not in a phylogenetic equilibrium. All available data suggest that the ultimate aim of genome restructuring in the plant cell, as in the eukaryotic cell in general, is the elimination of genome compartmentation while retaining physiological compartmentation.
The frozen accident. The evolutionary process of gene transfer was underway when something happened that stopped it. E.g. von Heijne, 1986.
It’s all a question of hydrophobicity. The five-helix rule. (Anon)
Some proteins (with co-factors) cannot be imported. (Anon)
Co-location for Redox Regulation - CORR (Allen 1993, 2003 et seq.)

23. Bioenergetic organelle
Endosymbiont
Bacterium

24. Proposed solution (hypothesis)
Why Mitochondria and Chloroplasts Have Their Own Genetic Systems
Co-location for Redox Regulation - CORR
Vectorial electron and proton transfer exerts regulatory control over expression of genes encoding proteins directly involved in, or affecting, redox poise.
This regulatory coupling requires co-location of such genes with their gene products; is indispensable; and operated continuously throughout the transition from prokaryote to eukaryotic organelle.
Organelles “make their own decisions” on the basis of environmental changes affecting redox state.
Allen, J. F. (1993) J. Theor. Biol. 165,
Allen, J. F. (2003) Phil. Trans. R. Soc. B458, 19-38

25. Prediction
Explanation of previous knowledge
Distribution of genes for components of oxidative phosphorylation between mitochondria and the cell nucleus

26. Redox regulation

27. Redox regulation

28. I II
III IV
ATPase
Mitochondrial matrix
Inter-membrane space

29. I II III IV ATPase Inter-membrane space NADH O2 H2O ADP NAD+ succinate
fumarate
ATP
Mitochondrial matrix

30. Redox regulation

32. The end. Fin. Really. Thank you for listening.