Bacterial metabolism

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Bacterial metabolism

• by
• E. Börje Lindström

This learning object has been funded by the
European Commissions FP6 BioMinE project
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Definitions
Metabolism
- all chemical reactions occurring in a cell

• With respect to function

• biosynthesis (anabolic reactions)
• energy production (catabolic reactions)

• exergonic reactions

- releases working energy (DG lt 0)

• endergonic reactions

- consumes energy (DG gt 0)

• co-enzyme

• a low-molecular-weight molecule, that
  participates in an enzymatic reaction
• excepts and donates electrons and functional
  groups

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Catabolism
ATP is produced by

• Photosynthesis

- light energy ? ATP

• Chemo synthesis

• chemical energy ? ATP
• substrate level phosphorylation
• oxidative phosphorylation
• red-ox reactions
• electron donator Ared ? Aox
• electron receiver Box ? Bred

• Processes in chemo synthesis

• Respiration
• Fermentation

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Respiration

• Box inorganic substance

• Model system

- glucose

• 4 processes

• Glycolysis
• Oxidative decarboxylation
• Krebs cycle (TCA)
• Electron transport chain

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Glycolysis
Embden-Meyerhof-Parnas pathway (EMP)

• Occurs in two steps

• Activation
• Oxidation (the carbon atom is oxidized)

• Summary of the reaction

Glucose 2 NAD ? 2 pyruvate 2 NADH 2 ATP
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Decarboxylation of pyruvate
2 pyruvate 2 NAD 2 CoASH ?
2 acetylSCoA 2 NADH
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Krebs cycle (TCA)

• 2 functions in the cell

• Catalyst in the energy metabolism
• Start material for biosynthesis of e.g. Amino
  acids

2 acetylSCoA
Krebs (TCA)
2 CO2
2 CO2
2 x 4 NADH
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Electron transport chain
Two (2) functions

• Transfer of electrons from NADH? Box
• produce ATP (oxidative phosphorylation)

• Mechanism

• H atoms from NADH is separated into
• e- (electrons) ? Box
• H (protons) ? outside of cytoplasm membrane
• pH gradient is produced (proton motive force,
  PMF)

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Box examples
Process Box

• aerobic respiration

- O2

• anaerobic respiration

• NO3-, NO2-
• SO42-, S0
• CO2

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Box examples, cont.
Lake
Bred
?
H2O
?
NO2- NH3 N2
Sediment
?
S2- (black sediment)
?
CH4 (methane)
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Fermentation

• Box is an organic substance
• often an internal substance
• the process is anaerobic
• no functional electron transport chain
• it can however exist in some micro-organisms

Model system
- Glucose
(Ox.)
?
(Red.)
Glucose
pyruvate
End products ( naming the process)
?
(3 alt.)
(7 alt.)
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Lactic acid fermentation
1) Homo-fermentative
EMP
?
Glucose
2 pyruvate 2 ATP 2 NADH
Ox.
Box
Red.
2 Lactic acid 2 NAD
Application

• Yoghurt
• Cheese
• Butter
• Sausages, etc.

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Lactic acid fermentation, cont.
2) Hetero-fermentative
-Phosphoketolase pathway (ox.step)
NADH
2 NADH
Ox.
?
?
Glucose
6-P-gluconate
Pyruvate acetylP CO2 ATP
Ox.
ATP
Red.
2 NAD
ethanol
NAD
Lactic acid
Summary
Glucose ? lactic acid ethanol CO2 ATP
Application

• Kefir, etc.

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Ethanol fermentation
Organism
- Saccharomyces cerevisiae (yeast)
EMP
?
Glucose
2 pyruvate 2 ATP 2 NADH
Ox.
CO2
2 acetaldehyde
(Box)
2 NAD
2 ethanol
Applications

• Wine
• Beer
• Vodka
• Bread

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Mixed acid fermentation
Bacteria

• E. coli

Salmonella
Shigella, etc.
Three (3) processes in the cell
1) glucose ? 2 pyruvate ? 2 lactic acid
2 ATP
ethanol
CO2 H2
?
2) glucose ? 2 pyruvate
CH3-COSCoA HCOOH
acetic acid ATP
2 ATP
CH3-COSCoA formic acid
(1)
3) glucose ? 2 pyruvate
succinate
(1)
2 ATP
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Mixed acid fermentation, cont.
Applications

• Diagnose of pathogenic bacteria (clinical
  bacteriology)
• Analysis of water in swimming pools etc.