electron transport chains electrons move from a carrier with a lower standard reduction potentials...
DESCRIPTION
E. coli electron transport chain Electrons move from: NADH FAD Coenzyme Q Terminal oxidase varies depending on growth conditions Amount of protons pumped out depends on growth conditionsTRANSCRIPT
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Electron transport chains
Electrons move from a carrier with a lower standard reduction potentials (EO) to a carrier with a higher EO
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Mitochondrial electron transport chain
Electrons eventually combine with 1/2 O2 and 2 H+ to form H2O
Protons pumped across the membrane at various points during electron transport
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E. coli electron transport chain
Electrons move from:
NADH FAD Coenzyme Q
Terminal oxidase varies depending on growth conditions
Amount of protons pumped out depends on growth conditions
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P. denitrificans electron transport chains
Has both aerobic and anaerobic electron transport chains
Anaerobic chain uses NO3- as the
final electron acceptor
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Oxidative phosphorylation
Is dependent on the proton motive force and chemiosmosis
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The proton motive force
Protons are pumped from the interior to the exterior of the membrane resulting in a gradient of protons and a membrane potential
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The roles of proton motive force
Powers rotation of bacterial flagella
Required for some types of active transport
Generation of ATP
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The roles of proton motive force
Flagella rotation Active transport
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Chemiosmosis
Diffusion of protons back across the membrane
drives the formation of ATP by ATP synthase
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ATP synthase
Composed of 2 components:
F0 - membrane embedded
F1- attached to inner membrane
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F0 component
Composed 1 a subunit, 2 b subunits and 9-12 c subunits
Electrons pass through a channel in F0 a subunit
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F1 component
Appears as a sphere on the inner membrane
Composed of 3 subunits, 3 subunits 2 subunits and 1 subunit
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F1 component
Passage of electrons through F0 causes subunit to rotate
Rotation causes conformational changes in subunits that results in the synthesis of ATP
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F1 component
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Yield of ATP in eukaryotic cells
1 NADH generates 2-3 ATPs
1 FADH2 generates 2 ATPs
Actual yield can be closer to 30 ATPs
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Yield of ATP in prokaryotic cells
Prokaryotic cells generate less ATP
Amounts vary depending on growth conditions
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Anaerobic respiration
Final electron acceptor is an inorganic molecule other than oxygen
Major electron acceptors are nitrate, sulfate and CO2
Metals and certain organic molecules can also be reduced
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Anaerobic respiration
Reduction of nitrate in respiration known as dissimilatory nitrate reduction
Nitrate often reduced sequentially to nitrogen gas (N2)
Process referred to as denitrification
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Carbohydrate catabolism
Glucose, fructose and mannose can enter glycolytic pathway after phosphorylation
Galactose is modified before being transformed into glucose-6-P
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Carbohydrate catabolism
Disaccharides and polysaccharides must be cleaved into monosaccharides
Can be cleaved by hydrolysis or phosphorolysis (results in the addition of a phosphate group)
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Carbohydrate catabolism
Reserve polymers like glycogen and starch are degraded by phosphorolysis to release glucose-1-P
Converted to glucose-6-P and enters glycolytic pathway
Poly--hydroxybutyrate converted to acetyl-CoA and enters the TCA cycle
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Lipid catabolism
Triacylglycerides are composed of glycerol and three fatty acids
Lipases separate glycerol from fatty acids
Glycerol phosphorylated and converted to dihydroxyacetone phosphate glyceraldehyde-3-P glycolysis
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Lipid catabolism
Fatty acids are converted to CoA esters and oxidized by the -oxidation pathway
Fatty acids degraded to acetyl-CoA TCA cycle
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Lipid catabolism
Fatty acids are converted to CoA esters and oxidized by the -oxidation pathway
Fatty acids degraded to acetyl-CoA TCA cycle
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-oxidation pathway
Produces
1. Acetyl-CoA
2. NADH
3. FADH2
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Protein and amino acid catabolism
Proteases hydrolyze proteins and polypeptides into amino acids
Removal of amino group referred to as deamination
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Deamination
Usually accomplished by transamination
Amino group transferred to an -keto acid acceptor
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Deamination
Organic acid oxidized for energy or used as carbon source
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Deamination
Excess nitrogen excreted as ammonium ion
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Oxidation of inorganic molecules (chemolithotrophy)
Chemolithotrophs derive energy from the oxidation of inorganic molecules
Most common electron donors are hydrogen, reduced nitrogen compounds, reduced sulfur compounds and ferrous iron (Fe2+)
Oxygen, nitrate and sulfate can be used as the final electron acceptor
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Oxidation of inorganic molecules (chemolithotrophy)
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Hydrogen oxidation
Several bacteria possess a hydrogenase enzyme that catalyzes the reaction:
H2 2H+ + 2e-
Electrons can be donated to an electron transport chain or NAD+
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Nitrogen oxidation
Species of Nitrosomonas and Nitrosospira oxidize ammonia to nitrite
NH4+ + 3/2 O2 NO2
- + H2O + 2H+
Species of Nitrobacter and Nitrococcus oxidize nitrite to nitrate
NO2- + 1/2 O2 NO3
-
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Nitrogen oxidation
Two genera working together can oxidize ammonia to nitrate
NH4+ + 2 O2 NO3
-
Process referred to as nitrification
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Nitrogen oxidation
Proton motive force can be used to produce ATP and NADH
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Sulfur oxidation
Some microorganisms can use reduced sulfur compounds as a source of electrons
Species of Thiobacillus oxidize sulfur-containing compounds to sulfuric acid (important environmental consequences)
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Sulfur oxidation
Can generate ATP by oxidative phosphorylation and substrate level phosphorylation
Substrate level phosphorylation requires the formation of adenosine 5-phosphosulfate (APS)
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Oxidation of inorganic molecules
Much less energy is available from the oxidation of inorganic molecules than from the oxidation of organic molecules