microbiology microbial metabolism ii catabolism &...

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MicrobiologyMicrobial Metabolism IICatabolism & AnabolismChing-Tsan Huang (黃慶璨)Office: Room 111, Agronomy HallTel: (02) 33664454E-mail: cthuang@ntu.edu.tw

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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