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MicrobiologyMicrobial Metabolism IICatabolism & AnabolismChing-Tsan Huang (黃慶璨)Office: Room 111, Agronomy HallTel: (02) 33664454E-mail: [email protected]
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CatabolismEnergy Release and ConservationProvide materials for biosynthesisAmphibolic pathways
AnabolismUse of Energy in BiosynthesisTurnoverCarefully regulated
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Amphibolic Pathways
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Source of Energy for MicroorganismsChemolithotrophyChemoorganotrophyPhototrophy
Chemical Energy
Work
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Chemoorganotrophic CatabolisnRespiration
Fermentation
AerobicRespiration
AnaerobicRespiration
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Chemoorganotrophic MetabolismAerobic respiration
using oxygen as exogenous electron acceptoryields large amount of energy, primarily by electron transport activity
Anaerobic respirationusing molecules other than oxygen as exogenouselectron acceptorsyields large amount of energy, primarily by electron transport activity
Fermentationusing endogenous electron acceptoroften occurs under anaerobic conditionslimited energy made available
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Overview of Aerobic Catabolism
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Carbohydrate Catabolism: Glucose PyruvateGlycolysis
Most commonAlso called Embden-Meyerhof pathwayOccurs in cytoplasmicmatrix of both procaryotes and eucaryotesGeneration of NADHATP synthesis via substrate-level phosphorylation
Glucose + 2 ADP + 2 Pi + 2 NAD+ 2 Pyruvate + 2 ATP + 2 NADH + 2 H+
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Carbohydrate Catabolism: Glucose Pyruvate
3 Glucose-6-P + 6 NADP+ + 3 H2O
2 Fructose-6-P + Glyceraldehyde-3-P + 3 CO2 + 6 NADPH + 6 H+
Pentose Phosphate Pathway
provide NADPH as source of electrons4-carbon sugar for aromatic amino acid synthesis and 5-carbon sugar for nucleic acid synthesis and CO2acceptorAerobic or anaerobic
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Carbohydrate Catabolism: Pyruvate CO2
TCA (tricaboxylicacid) cycle or Citric acid cycle orKreb’s cycle
FunctionProvide carbon skeletons for use in biosynthesis
AerobicUse O2 as e-
acceptor
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Electron Transport
Electron donors: NADH (3 ATPs) FADH2 (2 ATPs) Electron acceptor:Oxidative phosphorylation:process by which energy from electron transport is used to make ATP
Electron transport chainin the inner membrane of the mitochondrionin the bacterial plasma membrane
Wolinella succinogenes is a nonfermenting bacterium with fumurate as its sole carbon source. It undergoes anaerobic fumerate respiration.
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Carbohydrate Catabolism: Glucose CO2
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Fermentations
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Carbohydrate Catabolism: Pyruvate CO2
FermentationNo exogeneous e-
acceptorUse organic molecules as e-
acceptorATP formed by substrate-level phosphorylation
Anaerobic
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Lipid CatabolismLipid Fatty acid + Glycerol
Fatty acid β-oxidation
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Protein and Amino Acid CatabolismProtease
Hydrolysis of protein to amino acidsDeamination
Often occurs by transamination
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Principles Governing BiosynthesisMacromolecules are synthesized from limited number of simple structural units (monomers)
Many enzymes used for both catabolism and anabolism
Catabolic and anabolic pathways are not identical, despite sharing many enzymes
Breakdown of ATP coupled to certain reactions in biosynthetic pathways
Catabolic and anabolic pathways use different cofactors
Large assemblies (e.g., ribosomes) form spontaneously from macromolecules by self-assembly
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Energy Trapping: Photosynthesis
Light reactionlight energy is trapped and converted to chemical energy
Dark reactionreduce or fix CO2 and synthesize cell constituents
Oxygenic
Anoxygenic
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Light ReactionEucaryotes & Cyanobacteria
Green & Purple Bacteria
PMF
Reversed e- flow
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Photosynthetic Fixation of CO2Autotrophs obtain energy by trapping light during photo-synthesis or by oxidizing or reduced inorganic e- donorsCalvin, Calvin-Benson,
reductive pentosephosphoraltion cyclein eucaryotes, occurs in stroma of chloroplastin cyanobacteria, some nitrifying bacteria occur in carboxysomes
6 RuBP + 6 CO2
12 PGA
6 RuBP + Fructose 6-P
Carboxylation
Reduction
Regeneration
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Synthesis of Pyruvate to GlucoseGluconeogenesis: Heterotrophs synthesize sugars by reducing organic molecules
Glucoeogenesis Glycolysis
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Synthesis of Sugars and PolysaccharidesGluconeogenesis
synthesize glucose and fructose from noncarbohydrate precursors
Sugar nucleoside diphosphatessynthesis of other sugars , polysaccharides, and bacterial cell walls
ATP + glucose 1-P →ADP-glucose + PPi
(glucose)n + ADP-glucose →(glucose)n+1 + ADP
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Synthesis of Amino AcidsPrecursor metabolites used as starting substrates
carbon skeleton is remodeledamino group and sometimes sulfur are added
Nitrogen addition to carbon skeleton is importantpotential sources of nitrogen: ammonia, nitrate, or nitrogen
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Synthesis of Amino Acids
Oxaloacetate
Phosphoenolpyruvate
α-ketoglutarate
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Lipid SynthesisTriacrylglycerols & phospholipidsFatty acid synthesis
ACP: acryl carrier protein