View
216
Download
0
Category
Preview:
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 conditions
Citation preview
Electron transport chains
Electrons move from a carrier with a lower standard reduction potentials (EO) to a carrier with a higher EO
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
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
P. denitrificans electron transport chains
Has both aerobic and anaerobic electron transport chains
Anaerobic chain uses NO3- as the
final electron acceptor
Oxidative phosphorylation
Is dependent on the proton motive force and chemiosmosis
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
The roles of proton motive force
Powers rotation of bacterial flagella
Required for some types of active transport
Generation of ATP
The roles of proton motive force
Flagella rotation Active transport
Chemiosmosis
Diffusion of protons back across the membrane
drives the formation of ATP by ATP synthase
ATP synthase
Composed of 2 components:
F0 - membrane embedded
F1- attached to inner membrane
F0 component
Composed 1 a subunit, 2 b subunits and 9-12 c subunits
Electrons pass through a channel in F0 a subunit
F1 component
Appears as a sphere on the inner membrane
Composed of 3 subunits, 3 subunits 2 subunits and 1 subunit
F1 component
Passage of electrons through F0 causes subunit to rotate
Rotation causes conformational changes in subunits that results in the synthesis of ATP
F1 component
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
Yield of ATP in prokaryotic cells
Prokaryotic cells generate less ATP
Amounts vary depending on growth conditions
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
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
Carbohydrate catabolism
Glucose, fructose and mannose can enter glycolytic pathway after phosphorylation
Galactose is modified before being transformed into glucose-6-P
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)
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
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
Lipid catabolism
Fatty acids are converted to CoA esters and oxidized by the -oxidation pathway
Fatty acids degraded to acetyl-CoA TCA cycle
Lipid catabolism
Fatty acids are converted to CoA esters and oxidized by the -oxidation pathway
Fatty acids degraded to acetyl-CoA TCA cycle
-oxidation pathway
Produces
1. Acetyl-CoA
2. NADH
3. FADH2
Protein and amino acid catabolism
Proteases hydrolyze proteins and polypeptides into amino acids
Removal of amino group referred to as deamination
Deamination
Usually accomplished by transamination
Amino group transferred to an -keto acid acceptor
Deamination
Organic acid oxidized for energy or used as carbon source
Deamination
Excess nitrogen excreted as ammonium ion
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
Oxidation of inorganic molecules (chemolithotrophy)
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+
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
-
Nitrogen oxidation
Two genera working together can oxidize ammonia to nitrate
NH4+ + 2 O2 NO3
-
Process referred to as nitrification
Nitrogen oxidation
Proton motive force can be used to produce ATP and NADH
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)
Sulfur oxidation
Can generate ATP by oxidative phosphorylation and substrate level phosphorylation
Substrate level phosphorylation requires the formation of adenosine 5-phosphosulfate (APS)
Oxidation of inorganic molecules
Much less energy is available from the oxidation of inorganic molecules than from the oxidation of organic molecules
Recommended