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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
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  glyceraldehyde3-P  glycolysis
Lipid catabolism
Fatty acids are converted to
CoA esters and oxidized by
the -oxidation pathway
Fatty acids degraded to acetylCoA  TCA cycle
Lipid catabolism
Fatty acids are converted to
CoA esters and oxidized by
the -oxidation pathway
Fatty acids degraded to acetylCoA  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+ + 2eElectrons 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  NO3Process 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