Download Paracoccus denitrificans

Chapter 10
Metabolism: Energy
Release and Conservation
Sources of energy
•most microorganisms use
one of three energy sources
•the sun
•reduced organic
compounds
•reduced inorganic
compounds
•the chemical energy
obtained can be used to do
work
Figure 9.1
Chemoorganic fueling processesrespiration
• most respiration involves use of an electron transport
chain
• aerobic respiration
• final electron acceptor is oxygen
• anaerobic respiration
– final electron acceptor is different exogenous acceptor such
as NO3-, SO42-
• as electrons pass through the electron transport
chain to the final electron acceptor, a proton motive
force (PMF) is generated and used to synthesize
ATP
Chemoorganic fueling processes fermentation
• uses organic molecule that is part of the
pathway as the electron acceptor
• does not involve the use of an electron transport
chain nor the generation of a proton motive force
• ATP synthesized only by substrate-level
phosphorylation
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Catabolism of glucose – energy (ATP)
Cellular respiration
Aerobic respiration
Anaerobic respiration
Aerobic respiration – O2 is used
6C6H12O6 +6O2 > 6CO2 + 6H2O + energy
Glucose – oxidized – CO2
O2 reduced to water
Glycolysis, (Embden-Meyerhof) transition
reaction
• Krebs cycle, oxidative phosphorylation (electron
transport chain)
Glycolysis
Sugar splitting
Cytosol = liquid
Part of the cytoplasm
Each molec. Glucose
2 pyruvic acid + 2NADH + 4ATP
Cell gains only 2 ATP
Substrate level phosphorylation
Phosphate is added from a substrate
to
ADP
Amphibolic pathway – both
catabolically and anabolically
Transition reaction
Decarboxylated
oxidized
matrix of mitochondria
each molecule of glucose
2 acetyl CoA + 2NADH + 2 CO2
6NADH + 2 FADH2 + 4CO2 + 2 ATP
interact with the electron transport
chain located on the inner membrane
of mitochondria
electron transport chain – inner
membrane of mitochondria
The Electron Transport Chain
• series of electron carriers that operate
together to transfer electrons from NADH
and FADH2 to a terminal electron acceptor
Electron transport chain…
• as electrons transferred, energy
released
• in eucaryotes the electron transport
chain carriers are within the inner
mitochrondrial membrane
Power house – cellular respiration
DNA
70S ribosomes
intermembrane
space
oxidized
flavin mononucleotide FMN
chemiosmosis
ubiquinone Q
cytochrome cyt
oxidation of ETC
phosphorylation of ADP
Oxidative Phosphorylation
• Process by which ATP is synthesized
as the result of electron transport driven
by the oxidation of a chemical energy
source
Phosphorylation - addition phosphate
NADH – oxidized, electron transport chain is oxidized
• Proton Motive Force (PMF)
• Concentration gradient of protons
(chemical potential energy)
• Charge gradient (electrical potential
energy)
• Matrix is more alkaline and negative than
the intermembrane space
• Combined electrical and chemical
potential differences makes up the PMF
• chemiosmosis
Fig. 9.14a
PMF rotates the
ATP synthase
Conformation change
ADP and P can get to the
Catalytic site
ATP synthase
PMF drives ATP synthesis
• diffusion of protons back across
membrane (down gradient) drives
formation of ATP
• ATP synthase
– enzyme that uses PMF down gradient to
catalyze ATP synthesis
Procaryotic ETCs
• located in plasma membrane
• some resemble mitochondrial ETC, but
many are different
– different electron carriers
– may be branched
– may be shorter
Electron Transport Chain of E. coli
branched pathway
upper branch –
stationary phase and
low aeration
lower branch – log
phase and high
aeration
Figure 9.12
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Paracoccus denitrificans
Facultative anaerobe
Both aerobic and anaerobic
Gram negative
Found in the soil
ETC of Paracoccus
denitrificans - aerobic
Figure 9.16 (a)
ETC similar to mitochondrial ETC
ETC of P. denitrificans anaerobic
Figure 9.16 (b)
example of anaerobic respiration
An example…
• dissimilatory nitrate reduction
– use of nitrate as terminal electron acceptor
– the anaerobic reduction of nitrate makes it
unavailable to cell for assimilation or uptake
• denitrification
• reduction of nitrate to nitrogen gas
• in soil, causes loss of soil fertility
Microbial Fermentations
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oxidation of NADH produced by glycolysis
pyruvate or derivative used as electron acceptor
substrate only partially oxidized
oxygen not needed
oxidative phosphorylation does not occur
– ATP formed by substrate-level phosphorylation
Regeneration
Lactiobacillus
Saccharomyces
cerevisiae
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Lipids, proteins – used for energy
Triglyceride  glycerol + 3 fatty acids
Exoenzyme - lipase
Glycerol – dihydroxyacetone phosphate
Goes into glycolysis
Fatty acid  many units of acetyl CoA
Goes into Krebs cycle
Proteins – amino acids – proteases
AA – intermediates of glycolysis, Krebs
cycle
Chemolithotrophy
• carried out by chemolithotrophs (rock eaters)
• electrons released from energy source which is
an inorganic molecule
– transferred to terminal electron acceptor (usually O2 )
by ETC
• ATP synthesized by oxidative phosphorylation
• Electrons and energy from inorganic
Nitrifying bacteria
oxidize ammonia to nitrate
Nitrosomonas
Nitrobacter
Figure 9.25
NH3  NO2  NO3
requires 2 different genera
Fig. 9.24
Phototrophy
• photosynthesis
– energy from light trapped and converted to chemical
energy
– a two part process
• light reactions in which light energy is trapped and converted
to chemical energy
• dark reactions in which the energy produced in the light
reactions is used to reduce CO2 and synthesize cell
constituents
Photosynthesis
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Plants and algae – chloroplasts
6CO2 + 6 H2O  C6H12O6 +6O2
Light dependent reactions
Light independent reactions ( CalvinBenson reaction)
Table 9.5
oxygenic photosynthesis – eucaryotes and cyanobacteria
anoxygenic photosynthesis – all other bacteria
The Light Reaction in Anoxygenic
Photosynthesis
• H2O not used as an electron source; therefore
O2 is not produced
• carried out by phototrophic green bacteria,
phototrophic purple bacteria and heliobacteria
• In general obligate anaerobes
• H2S electron source
• Chromatium
Bacteriorhodopsin-Based Phototrophy
• Some archaea use a type of phototrophy that
involves bacteriorhodopsin, a membrane protein
which functions as a light-driven proton pump
• a proton motive force is generated
• an electron transport chain is not involved
• Halobacterium salinarium
• Oxygen aerobic
• No oxygen high light intensity makes
bacteriorhodopsin
Pumps proton
noETC
Halobacterium
archaea
Figure 9.27
Flow of energy
sunlight
CO2 + water ---------- glucose
ATP --- energy
Synthesis, transport, movement
Sun is the ultimate source of energy