Mitochondria and chloroplasts

SBS922 Membrane Biochemistry

John F. Allen

School of Biological and Chemical Sciences, Queen Mary, University of London

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http://jfa.bio.qmul.ac.uk/lectures/

The chemiosmotic theory

The membrane energised state

We have seen how observed characteristics of oxidative phosphorylation led to conclusion that there was a membrane energised state linking electron transfer in mitochondria to ATP synthesis and other membrane-linked energy-dependent functions such as active transport of solutes.

Electron transport ATP synthesisEnergisedState…

What is the “energised state”….?

CHEMIOSMOTIC HYPOTHESIS

 

Proposed by Peter Mitchell 1961 and further elaborated 1966

 

Competing hypotheses

1) Chemical hypothesis (i.e. like substrate-level phosphorylation)

2) Conformational hypothesis

3) Localised proton hypothesis (variation of chemiosmotic)

 

Transmembrane Proton gradient

Energy transduction occurs via a proton circuit which circulates through the insulating coupling membrane and the two adjacent bulk phases (the matrix and the cytosol/ intermembrane space in mitochondria).

Since each of the two bulk phases is in equilibrium, energy storage is transmembrane rather than intramembrane.

I II III IV ATPase

Mitochondrial matrix

Inter-membrane space

H+ H+ H+

H+

NADH O2

ATP

ADP

H2O

NAD+ succinate fumarate

ATPase

Also known as “ATP Synthase”

F-ATPases (c.f. V-ATPases; P-ATPases)

- F1

- Fo

ATP + H2O ADP + Pi

F1

F1

Figure from: ALLEN, J F (2002) Photosynthesis of ATP - Electrons, Proton Pumps, Rotors, and Poise. Cell 110, 273–276

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http://www.res.titech.ac.jp/~seibutu/

25http://www.res.titech.ac.jp/~seibutu/

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Fo

F1

Fo

http://jfa.bio.qmul.ac.uk/~john/webstar/ltm/06/3ATP.html

Rotation of the Fo-ATPase.Fo-ATPase as a proton-driven, rotary stepping motor, as proposed by Junge (1997).

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The F1-Fo ATPase

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http://www.biologie.uni-osnabrueck.de/Biophysik/Junge/overheads.html

http://jfa.bio.qmul.ac.uk/lectures/http://jfa.bio.qmul.ac.uk/lectures/

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