Download Bacterial metabolism

Bacterial metabolism
by
E. Börje Lindström
This learning object has been funded by the European Commissions FP6 BioMinE project
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 < 0)
• endergonic reactions:
- consumes energy (DG > 0)
• co-enzyme:
-a low-molecular-weight molecule, that participates in
an enzymatic reaction
- excepts and donates electrons and functional groups
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
Respiration
• Box = inorganic substance
• Model system:
• 4 processes:
- glucose
1)
Glycolysis
2)
Oxidative decarboxylation
3)
Krebs cycle (TCA)
4)
Electron transport chain
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
Decarboxylation of pyruvate
2 pyruvate + 2 NAD+ + 2 CoASH 
2 acetyl~SCoA + 2 NADH
Krebs cycle (TCA)
• 2 functions in the cell:
1)
Catalyst in the energy metabolism
2)
Start material for biosynthesis of
e.g. Amino acids
2 acetyl~SCoA
Krebs
(TCA)
2 CO2
2 CO2
2 x 4 NADH
Electron transport chain
-Transfer of electrons from NADH Box
Two (2) functions:
- produce ATP (oxidative phosphorylation)
Ared
Aox
NAD+
FADH2
CYT.
……
NADH
FADH+
ATP
• Mechanism:
Bred
Box
ATP ATP
-H atoms from NADH is separated into
- e- (electrons)  Box
- H+ (protons)  outside of cytoplasm membrane
- pH gradient is produced (proton motive force, PMF)
Box examples
Process
Box
• aerobic respiration:
- O2
• anaerobic respiration:
- NO3-, NO2- SO42-, S0
- CO2
Box examples, cont.
Lake
Bred
O2
NO3-
Sediment


H2O
NO2- ; NH3 ; N2
SO42-

S2- (black sediment)
CO2

CH4 (methane)
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.)
(3 alt.)
- Glucose
pyruvate

(Red.)
End products
(7 alt.)
( naming the process)
Lactic acid fermentation
1) Homo-fermentative:
Glucose
EMP

Ox.
2 pyruvate + 2 ATP + 2 NADH
Box
Red.
2 Lactic acid + 2 NAD+
Application:
- Yoghurt
- Cheese
- Butter
- Sausages, etc.
Lactic acid fermentation, cont.
2) Hetero-fermentative:
-Phosphoketolase pathway (ox.step)
NADH
Glucose

ATP
2 NADH
6-P-gluconate
Ox.

Ox.
Pyruvate +acetyl~P + CO2 + ATP
Red.
2 NAD+
ethanol
Lactic acid
Summary:
Application:
NAD+
Glucose  lactic acid + ethanol + CO2 + ATP
-Kefir, etc.
Ethanol fermentation
Organism:
Glucose
EMP

Ox.
- Saccharomyces cerevisiae (yeast)
2 pyruvate + 2 ATP + 2 NADH
CO2
2 acetaldehyde (Box)
2 NAD+
2 ethanol
Applications:
-Wine
- Beer
- Vodka
- Bread
Mixed acid fermentation
Bacteria:
- E. coli;
Salmonella;
Shigella, etc.
Three (3) processes in the cell:
2 NAD+
2NADH
2 NAD+
1) glucose  2 pyruvate  2 lactic acid
2 ATP
2 NAD+
2 NADH
ethanol
2 NAD+
2NADH
2) glucose  2 pyruvate
 CH3-CO~SCoA + HCOOH
2 ATP
2 NAD+
2NADH
3) glucose  2 pyruvate
2 ATP
CO2 + H2
acetic acid + ATP
CH3-CO~SCoA + formic acid
(1)
2NADH
(1)
2 NAD+
succinate
Mixed acid fermentation, cont.
Applications:
- Diagnose of pathogenic bacteria (clinical bacteriology)
- Analysis of water in swimming pools etc.