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21 Cards in this Set
- Front
- Back
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OXIDATIVE PHOSPHORYLATION
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The Respiratory Electron Transport System – Part I
• Consists of a series of membrane-associated electron carriers - In prokaryotes they are found in the cell membrane - In eukaryotes they are found in the inner mitochondrial membrane • The sequential transfer of electrons from one ETS carrier to the next yields energy to pump protons across the membrane - Electrons are transported through the ETS from carriers with more negative Eo′ to those with more positive Eo′ - The terminal electron acceptor is 02 - Note: Eo′ is the standard reaction potential - It is a value that indicates the ability of a molecule to gain or lose electrons |
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Proton Motive Force and Chemiosmotic ATP Generation
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Peter Mitchell • The accumulation of H+ on one side of the membrane results in the generation of a proton motive force (or proton potential. p has two components1) An H+ gradient 2) A charge difference
• These cause the membrane to be energized with potential energy, in effect a “proton battery” |
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Proton Motive Force and Chemiosmotic ATP Generation II
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• The membrane is basically impermeable to protons
=> Gradient does not automatically dissipate - ATP synthase protein complex contains channels for proton entry - As protons push in through this channel, the potential energy is used to generate ATP • The chemiosmotic theory is summarized in Fig. 14.5 |
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The Respiratory Electron Transport System – Part II
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• The reduced coenzymes NADH and FADH2 carry high-energy electrons derived from glucose
• The ETS carriers harvest the reducing potential of these electrons in steps - Otherwise most of the energy would be lost as heat • Cofactors associated with the ETS carriers are responsible for these small, reversible redox changes - These contain either or both of these molecular structures 1) Metal ions such as iron or copper that are held in place by amino acids. - Example: iron-sulfur proteins 2) Conjugated double bonds and heteroaromatic rings ex. flavin mononucleotide- Please refer to Fig. 14.12 |
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• Note: ETS carriers are said to be because they oxidize one substrate (electrons) and reduce another ( electrons)
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oxidoreductase/remove/donate
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• A respiratory ETS is made up of at least three different functional components:
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- i) A substrate dehydrogenase; ii) A mobile electron carrier; and iii) A terminal oxidase
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The F1F0 ATP synthase
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• The F1F0 ATP synthase is a protein complex that is highly conserved in the bacterial cell membrane, the mitochondrial inner membrane, and the chloroplast thylakoid membrane
• It is composed of two complexes - F0 = Embedded in the membrane Made up of 12 identical c subunits Pumps protons - F1 = Protrudes into the cytoplasm Made up of three pairs of and subunits Generates ATP - The two complexes are connected by a central stalk () which extends through F1 - Serves as an - The knob is anchored to the membrane by a peripheral stalk made up of the a and b subunits - Please refer to Fig. 14.18 |
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The F1F0 ATP synthase steps
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• The process of ATP synthesis can be summarized as such:
1) Three protons enter the C subunits of the F0 complex 2) The F0 complex rotates 1/3rd of a turn relative to the F1 complex 3) The protons are released into the cytoplasm 4) The F1 complex does not rotate - However, it changes conformation, thus allowing for the synthesis of a molecule of ATP from ADP PI- Please refer to Fig. 14.19 |
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Messing Up Chemiosmosis
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• There are two classes of chemicals that interfere with chemiosmosis
1. Inhibitors = Block transport of electrons through the ETS to O2 - Examples Cyanide 2. Uncouplers = Prevent the synthesis of ATP but do not interfere with electron transport - Examples 2,4 dinitrophenol |
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The Proton Potential Drives Many Cell Functions
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rotation of flagella, uptake of nutrients, efflux of drugs
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Na+ Pumps: An Alternative to H+ Pumps
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• Some organisms have evolved an ETS that pumps Na+ instead of H+
• The sodium motive force is analogous to the proton motive force in that includes the electric potential and the sodium ion concentration gradient• For example: - Halophilic archaea- halococcus - Human pathogens- vibro cholera - yersinia pestis |
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The Archaeal ATP synthase
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• The ATP synthase from Archaea differs a little from that of bacteria and eukarya
- For example, it has more subunits • It has been dubbed the A1A0 ATP synthase |
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ATP YIELD FROM AEROBIC OXIDATION OF GLUCOSE
EMP Pathway of Glycolysis - Substrate-level phosphorylation (ATP) - Oxidative phosphorylation with 2 NADH |
2ATP/6ATP
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ATP YIELD FROM AEROBIC OXIDATION OF GLUCOSE
2 Pyruvate to 2 Acetyl-CoA Oxidative phosphorylation with 2 NADH |
6 ATP
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ATP YIELD FROM AEROBIC OXIDATION OF GLUCOSE
-Tricarboxylic Acid Cycle- Substrate-level phosphorylation (GTP)- Oxidative phosphorylation with 6 NADH- Oxidative phosphorylation with 2 FADH2 |
2 ATP/18ATP/4ATP
Total generated overall 38 ATP |
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ANAEROBIC RESPIRATION
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• A mechanism of ATP generation that is unique to prokaryotes
• It is similar to aerobic respiration - The difference is that the TEA in the electron transport chain is a chemical compound other than o2 • Respiring prokaryotes typically contain several differed terminal oxidoreductases • Anaerobic respiration is NOT as efficient in ATP synthesis as aerobic respiration - The magnitude of the change in reduction potential is a direct indication of the amount of free energy released - Please refer to Table 14.1 |
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• Respiring prokaryotes typically contain several differed terminal
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oxidoreductases
- These enzymes are conventionally termed “reductases” to emphasize the reduction of the alternative electron acceptor - However, in any given environment, the strongest electron donor-acceptor pair is used! |
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• The vast majority of these alternative TEAs are inorganic
- Two major exceptions |
- Fumarate, which is reduced to Succinate
- Trimethylamine oxide, which is reduced to trimethylamine |
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• Oxidized forms of nitrogen
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- Nitrate is an important alternative TEA
- It is successively reduced by many bacteria as follows NO3– → NO2– → NO → 1/2 N2O → 1/2 N2 - In general, any given species can only carry out one or two transformations in the series- Organism =E. coli |
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- Alternatively, many soil bacteria reduce nitrite to
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ammonium
NO2– + 8 H+ → NH4+ + 2 H2O- Organism = bacillus sp |
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Oxidized forms of sulfur
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- Sulfate-reducing prokaryotes are widespread in marine habitats, where sulfate is the most common
anion after chloride - Organism = desulfovibro desulfuricans |
