the proton motive force
DESCRIPTION
The transfer of H + through a proton pump generates an electrochemical gradient of protons, called a proton motive force. The Proton Motive Force. - It drives the conversion of ADP to ATP through ATP synthase. - This process is known as the chemiosmotic theory. Figure 14.5. - PowerPoint PPT PresentationTRANSCRIPT
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• The transfer of H+ through a proton pump generates an electrochemical gradient of protons, called a proton motive force.
The Proton Motive Force
Figure 14.5
- It drives the conversion of ADP to ATP through ATP synthase.
- This process is known as the chemiosmotic theory.
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• When protons are pumped across the membrane, energy is stored in two different forms:
• - The electrical potential (Dy) arises from the separation of charge between the cytoplasm and solution outside the cell membrane.
• - The pH difference (DpH) is the log ratio of external to internal chemical concentration of H+.
• The relationship between the two components of the proton potential Dp is given by:
• Dp = Dy – 60DpH
The Proton Motive Force
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Figure 14.6
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• Besides ATP synthesis, Dp drives many cell processes including: rotation of flagella, uptake of nutrients, and efflux of toxic drugs.
Dp Drives Many Cell Functions
Figure 14.9
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• ETS proteins such as cytochromes associate electron transfer with small energy transitions, which are mediated by cofactors.
• Energy transitions typically involve these kinds of molecular structures:
• - Metal ions, such as iron or copper, held in place with amino acid residues
• - Conjugated double bonds and heteroaromatic rings, such as the nicotinamide ring of NAD+/NADH
The Respiratory ETS
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Figure 14.11
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Figure 14.13
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A Bacterial ETS for Aerobic NADH Oxidation
Figure 14.14
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• Animation: A bacterial electron transfer system
Click box to launch animation
ETS
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• The F1Fo ATP synthase is a highly conserved protein complex, made of two parts:
The F1Fo ATP Synthase
- Fo: Embedded in the membrane
- Pumps protons
- F1: Protrudes in the cytoplasm
- Generates ATP
Figure 14.17
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H+ Flux Drives ATP Synthesis
Figure 14.18AB
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• Animation: ATP Synthase Mechanism
Click box to launch animation
The F1Fo ATP Synthase
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• Oxidized forms of nitrogen• - Nitrate is successively reduced as follows:
• NO3– → NO2
– → NO → 1/2 N2O → 1/2 N2
nitrite nitric oxide
nitrous oxide
- In general, any given species can carry out onlyone or two transformations in the series.
Oxidized forms of sulfur- Sulfate is successively reduced by many bacteria as follows:
SO42– → SO3
2– → 1/2 S2O32– → S0 → H2S
sulfite thiosulfate sulfur hydrogen sulfide
nitrate nitrogen gas
sulfate
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• Anaerobic environments, such as the bottom of a lake, offer a series of different electron acceptors.
• - As each successive TEA is used up, its reduced form appears; the next best electron acceptor is then used, generally by a different microbe species.
Figure 14.20
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• Lithotrophy is the acquisition of energy by oxidation of inorganic electron donors.
• A kind of lithotrophy of great importance in the environment is nitrogen oxidation.
Lithotrophy
NH4+ → NH2OH → HNO2 → HNO3
ammonium hydroxylamine nitrous acid(nitrite)
nitric acid(nitrate)
1/2 O2 O2 1/2 O2
Surprisingly, ammonium can also yield energy under anaerobic conditions through oxidation by nitrite produced from nitrate respiration.
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• Hydrogenotrophy is the use of molecular hydrogen (H2) as an electron donor.
Hydrogenotrophy
- H2 has sufficient reducing potential to donate e– to nearly all biological electron acceptors.
- Including chlorinated organic molecules, via dehalorespiration
- Which has potential for bioremediation Figure 14.24