mitochondria and chloroplasts
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SBS922 Membrane Biochemistry. Mitochondria and chloroplasts. John F. Allen School of Biological and Chemical Sciences, Queen Mary, University of London. 1. http://jfa.bio.qmul.ac.uk/lectures/. The chemiosmotic theory. The membrane energised state - PowerPoint PPT PresentationTRANSCRIPT
Mitochondria and chloroplasts
SBS922 Membrane Biochemistry
John F. Allen
School of Biological and Chemical Sciences, Queen Mary, University of London
1
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)
Mitchell proposed that electron transfer directly produced an electrochemical gradient of protons across the coupling membrane that was subsequently used to drive ATP synthesis. The theory was subsequently adapted and expanded, principally by Mitchell and his colleague Jennifer Moyle to account for other membrane-linked energy dependent functions such as the active transport of solutes across the membrane.
The chemiosmotic hypothesis is named because it is postulated to involve both
a) chemical reactions, the transfer of chemical groups (electrons,protons and O2
2-) within the membrane
b) osmotic reactions, the transport of a solute (protons) across the membrane
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 (intramembrane proton gradients were the basis of the localised proton hypothesis).
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 ADP + Pi
F1
Figure from: ALLEN, J F (2002) Photosynthesis of ATP - Electrons, Proton Pumps, Rotors, and Poise. Cell 110, 273–276
Fo
http://plantcell.lu.se/ltm/06/3ATP.html
Rotation of the Fo-ATPase.Fo-ATPase as a proton-driven, rotary stepping motor, as proposed by Junge (1997).
The F1-Fo ATPase
http://www.biologie.uni-osnabrueck.de/Biophysik/Junge/overheads.html
http://www.biologie.uni-osnabrueck.de/Biophysik/Junge/pictures/AviRLE256_240_25.avi
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http://jfa.bio.qmul.ac.uk/lectures/