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8- Microbial Metabolism
Metabolism
ATP / ADP / AMP
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(See Table 8.2 for some cofactors)
Enzyme structure simple non-protein: ribozyme
examples of Holoenzymes
What catalysts do
(eg: enzymes)
Energy released
(Enzyme is NOT used up)
substrates
products
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optimum optimum
Affecting enzyme function
Inhibition
(allosteric site)
Metabolic pathway control by feedback inhibition
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Metabolic pathway control by gene expression
Redox reactions
In many biological redox reactions:
electrons are usually passed along as part of H atoms
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Substrate-level phosphorylation
Oxidative- or Photo-phosphorylation
Glucose Catabolism
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Glycolysis = Embden-Meyerhoff pathway
Glycolysis (cont.) (occurs in cytoplasm)
Energy-investment stage
Energy-conserving stage
Glycolysis alternative:
Pentose-phosphate pathway
can use glucose
makes & uses pentoses & other useful substrates for biosynthesis
produces 2 NADPH/ glucose & 1 ATP (through glycolysis)
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Glycolysis alternative:
Entner-Doudoroff pathway
uses glucose
produces 1 ATP & 1 NADPH & 1 NADH/glucose
in prokaryotes only
Fate of pyruvate
Kreb’s cycle/
Citric Acid cycle/
TCA cycle
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Transition/preparatory step reaction In mitochondrial matrix
energy
oxidative -> ETC
phosphorylation -> chemiosmosis
Electron Transport Chain/System
Chemiosmosis
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Energy summary for aerobic respiration
Anaerobic Respiration: different final electron acceptor
acceptor product
nitrate (NO3-) -> nitrite (NO2
-)
-> nitrous oxide (N2O)
-> nitrogen gas (N2)
(eg: Pseudomonas, Bacillus)
sulfate (SO42-) -> hydrogen sulfide (H2S)
(eg: Desulfovibrio)
carbonate (CO3-) -> methane (CH4)
(eg: Methanogenium)
homolactic alcoholic
Fermentation ≠ Anaerobic Respiration
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Fermentation: others
Other kinds of catabolism
Anabolism (= biosynthesis)
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Halobacterium (Archaea)
Photosynthesis group PS pigments(s) 1) purple S bacteriochlorophylls a or b 2) purple non-S bacteriochlorophylls a or b ---------------------------------------------------------- 3) green S bacteriochlorophylls a + c,
d, or e 4) green non-S bacteriochlorophylls a + c ---------------------------------------------------------- 5) heliobacteria bacteriochlorophyll g ---------------------------------------------------------- 6) Halobacterium bacteriorhodopsin ---------------------------------------------------------- 7) cyanobacteria chlorophyll a + phycobilins ---------------------------------------------------------- 8) PS-protists chlorophyll a + various 9) almost all chlorophyll a + b land plants
Chloroplast anatomy & the 2 sets of reactions
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Overall:
6 CO2 + 12 H2O
in the presence of light & chlorophyll a yields
C6H12O6 + 6 O2 + 6 H2O
Light Dependent Reactions:
12 H2O + 12 NADP+ + 18 ADP + 18 phosphates with light and chlorophyll a yields:
6 O2 + 12 NADPH + 18 ATP
Light Independent Reactions:
12 NADPH + 18 ATP + 6 CO2 yields:
C6H12O6 (glucose) + 12 NADP+ + 18 ADP + 18 phosphates + 6 H2O
Light Dependent Reactions
chloroplast
In eukaryotic chloroplasts & cyanobacteria there are 2 kinds of photosystems: I & II
Other light-harvesting pigments
Light-Dep. Reactions: Non-cyclic photophosphorylation
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Light-Dep. Reactions: Cyclic photophosphorylation
Carbon fixation = making sugars
From non-cyclic
From cyclic
Chemosynthesis: Using the energy from inorganic chemicals to build sugars from CO2; an alternative to photosynthesis.
Only some prokaryotes can do this.
Is done where there is no light, but can be done where there is light.
One example: sulfur bacteria
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Metabolism is
1) integrated and
2) many pathways, not all, are amphibolic
To see more about metabolism (including animations):
IUBMB-Nicholson Metabolic Maps, Minimaps & Animaps http://www.iubmb-nicholson.org/
More advanced
http://www.genome.jp/kegg/pathway.html