Transcript Chapter 1 Art Slides - Cal State LA

Chapter 14
Lecture Outline
Respiration, Lithotrophy,
and Photolysis
Common Principles of Respiration,
Lithotrophy and Photolysis


Electron transport system (electron transport chain)
Electron transfer reactions (oxidation-reduction
reactions)





A is oxidized, B is reduced
Energy of electron flow powers the cell
Storage of energy from electron transfer in form of an
electrochemical potential (voltage) across the membrane
Voltage potential includes a concentration gradient of
ions (H+, Na+) plus charge difference
Voltage potential drives ATP synthesis and other
processes
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Electricity from Iron-Reducing
Bacterium
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Soil bacteria
commonly oxidize
organic nutrients
Geobacter
metallireducens
transfers electrons to
iron ions (F3+) via their
pili
Pili act as nanowires
Can power an
electrical clock
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Distinction of Respiration,
Lithotrophy and Photolysis

Respiration

Organic molecules are electron donors (oxidation of organic
electron donors)
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

Final electron acceptor is oxygen (aerobic respiration) or
inorganic molecules (anaerobic respiration)
Lithotrophy

Inorganic molecules are electron donors (oxidation of
inorganic electron donors)



Sugars, lipids, amino acids
Fe2+ , H2
Final electron acceptor is oxygen or inorganic molecule
Photolysis

Light capture coupled to splitting of H2S or H2O
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How does Fermentation fit in?
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Electrons passed to electron acceptors
 Respiration

Electrons passed to through electron transport
system to inorganic acceptors
Aerobic respiration: O2
 Anaerobic respiration: nitrogen, sulfur compounds

 Fermentation

Electrons passed to organic receptors without
electron transport system
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Refresh Once More the Sources of
Energy, Electrons, and Carbon

Energy
 photo-

Electrons
 litho-

(light) vs. chemo-
(inorganic) vs. organo-
Carbon
 auto-
(CO2) vs. hetero- (all else)
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Electron Transport Systems

Electron transport occurs on membranes
 Electron
acceptor usually present outside cell
(exogenous)

Needed in large quantities for respiration
 Electron
passage energy must be captured by cell
cytoplasm

Inner (cell) membrane of bacteria, archaea
 Inner
membrane of
mitochondria, chloroplasts
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Selenium granule deposited
at inner membrane
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Members of an Electron Transport
System (ETS)
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
NADH or other electron donor
Electrons
Oxidoreductase protein complexes

Cytochromes






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Colored proteins
Absorbance spectrum shifts with change in redox state
Cytochrome C Oxidase detected in clinical diagnostic kits
Cofactors like FMN
Quinones
Terminal oxidase
Terminal electron acceptor
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The Respiratory ETS

Electrons from NADH  O2 release energy
 Too
much energy to capture in one step
 Requires intermediates
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
Multiple steps
Common features in many ETS pathways
 NADH
Oxidase
 Quinones
 Cytochromes
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Electron Transport is Coupled to
Proton Transport
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Sequential electron transfer yields energy to
pump ions across the membrane
Most often H+
Proton concentration gradient is established
Concentration gradient plus charge
(chemiosmosis) difference creates proton motive
force
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The Proton Motive Force

Energy of electron transport is captured
 As

a gradient across a membrane
Gradient of protons
 Charge

and concentration of electrons
Drives protons out of cell
 Gradient
of protons has
charge, concentration

Both tend to drive
protons back into cell
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The Chemiosmotic Hypothesis
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
Electron transport
system pumps protons
out of the cell
Resulting
electrochemical
gradient of protons
drives conversion of
ADP to ATP through
ATP synthase
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Processes Driven by Proton Motive
Force
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ATP Synthase
Uptake of
nutrients
Drug efflux
pumps
Flagellar
rotation
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ATP Synthase (ATPase)
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
Flux protons is
coupled to
converting ADP +
Pi to ATP
F0
Protons enter c subunits
of the F0 complex

The F0 subunits
rotate relative to
the F1 complex
ADP + Pi
F1
ATP
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E. coli Respiratory ETS
Animation: A Bacterial Electron Transport
System
Click box to launch animation
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Proton Potential Creates ATP
Animation: ATP Synthase Mechanism
Click box to launch animation
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Anaerobic Respiration
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Many environments lack oxygen
 Gut,
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deep soil, deep ocean
Less energy producing than aerobic respiration
Use other terminal electron acceptors
 Nitrogen
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compounds
NO3- + 2e- + 2H+  NO2- + H2O
2 NO2- + 2e- + 4H+  2 NO + 2H2O
2 NO + 2e- + 2H+  N2O + H2O
N2O + 2e- + 2H+  N2 + H2O
NO2- + 6e- + 8H+  NH4+ + 2H2O
Funnels into nitrogen oxidation
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Lithotrophy
Reduced minerals serve as electron
donors for an electron transport system
 Only prokaryotes can grow by
metabolizing inorganic compounds without
photosynthesis

 Fill
many key niches in ecosystems
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Examples for Lithotrophy

Nitrogen oxidation
 Anaerobic
ammonium oxidation plays major role in
waste water treatment

Sulfur oxidation
 production
of sulfuric acid
 Supplemental to commercial mining


Metal oxidation
Hydrogenothrophy
 Oxidation
of H2 by sulfur leads to H2S
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Methanogenesis
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Methanogenesis

Reduction of CO2 and other single carbon
compounds to methane
 Metabolized

by methanotrophs
Only observed in a special group of archaea
 Methanogens

Found in
 Landfills
 Natural methane gas can be harvested
 Intestine of cows and humans
 Deep
oceans
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Do not Confuse

Methanogens
 Generate

Methanotrophs
 Oxidize

methane
(metabolize) methane
Methylotrophs
 Oxidize
single C molecules other than
methane such as methanol or methylamine
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Phototrophy and Photolysis
Phototrophy: all forms of energy yielding
metabolism that involve absorption of light
energy
 Photolysis: light absorption coupled to
splitting an electron from a molecule
 Photosynthesis: photolysis with CO2
fixation and biosynthesis

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Photolysis
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Photoexcitation of a light absorbing pigment
leads to electron transfer through an ETS
Light-driven separation of electrons from a
molecule
Electron passes to quinols
 From
quinols to cytochromes
 Energy of passage pumps H+ outside membrane


Photolytic ETS generates a proton potential and
the reduced cofactor NADH
Photolytic proton potential drives ATP synthase
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Lightabsorbing Pigments Used in
Prokaryots
Chlorophyll (in cyanobacteria)
 Bacteriochlorophyll
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 In

Conduct photolysis
green and purple bacteria
Caretenoid
 Accessory
pigment used by purple bacteria
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Common Principle of Photolysis
Membrane embedded chain of
oxidoreductases and quinones
 Common design

 Antenna
system
 Reaction center complex
 ETS
 Energy carriers
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Photolytic Electron Transport Chain

Three systems
 Photosystem
I
 Photosystem II
 Oxygenic Z pathway
Includes PSI and II components
 Molecular oxygen is generated
 Only in cyanobacteria (and green plants)
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