Bacterial metabolism

by

E. Börje Lindström

This learning object has been funded by the European Commissions FP6 BioMinE project

DefinitionsMetabolism: - all chemical reactions occurring in a

cell

• With respect to function: -biosynthesis (anabolic reactions)

- energy production (catabolic reactions)

• exergonic reactions: - releases working energy (G < 0)

• endergonic reactions: - consumes energy (G > 0)

• co-enzyme: -a low-molecular-weight molecule, that participates in an enzymatic reaction

- excepts and donates electrons and functional groups

CatabolismATP 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: - glucose

• 4 processes: 1) Glycolysis

2) Oxidative decarboxylation

3) Krebs cycle (TCA)

4) Electron transport chain

Glycolysis

• Occurs in two steps: -Activation

- Oxidation (the carbon atom is oxidized)

• Summary of the reaction:

Glucose + 2 NAD 2 pyruvate + 2 NADH + 2 ATP

Embden-Meyerhof-Parnas pathway (EMP)

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

Krebs (TCA)

2 acetyl~SCoA

2 CO2

2 CO2

2 x 4 NADH

Electron transport chain

Ared

Aox Box

Bred

NAD+

NADH

FADH2

FADH+

CYT.……

Two (2) functions: -Transfer of electrons from NADH Box

- produce ATP (oxidative phosphorylation)

ATP ATPATP

• 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)

Box examples

Process Box

• aerobic respiration: - O2

• anaerobic respiration: - NO3-, NO2

-

- SO42-, S0

- CO2

Box examples, cont.

O2

Sediment

NO3-

SO42-

CO2

Bred

NO2- ; NH3 ; N2

S2- (black sediment)

CH4 (methane)

Lake

H2O

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

Glucose pyruvate End products

( naming the process)

(Ox.) (Red.)

(3 alt.) (7 alt.)

Lactic acid fermentation

Glucose EMP

2 pyruvate + 2 ATP + 2 NADHOx. Box

2 Lactic acid + 2 NAD+

1) Homo-fermentative:

Application: - Yoghurt

- Cheese

- Butter

- Sausages, etc.

Red.

Lactic acid fermentation, cont.

2) Hetero-fermentative: -Phosphoketolase pathway (ox.step)

Glucose 6-P-gluconate Pyruvate +acetyl~P + CO2 + ATPNADH

ATP

2 NADH

Ox.

Ox.

Lactic acid NAD+

ethanol

2 NAD+Red.

Summary: Glucose lactic acid + ethanol + CO2 + ATP

Application: -Kefir, etc.

Ethanol fermentationOrganism: - Saccharomyces cerevisiae (yeast)

GlucoseEMP

2 pyruvate + 2 ATP + 2 NADHOx.

2 acetaldehyde

CO2

(Box)

2 ethanol2 NAD+

Applications: -Wine

- Beer

- Vodka

- Bread

Mixed acid fermentation

Bacteria: - E. coli; Salmonella; Shigella, etc.

Three (3) processes in the cell:

1) glucose 2 pyruvate 2 lactic acid

CH3-CO~SCoA + HCOOH

CH3-CO~SCoA + formic acid

ethanol2 NADH2 NAD+

2) glucose 2 pyruvate

2 NAD+ 2NADH 2 NAD+

acetic acid + ATP

CO2 + H22NADH2 NAD+

3) glucose 2 pyruvate2NADH2 NAD+ (1)

(1)

2NADH 2 NAD+

succinate

2 ATP

2 ATP

2 ATP

Mixed acid fermentation, cont.

Applications: - Diagnose of pathogenic bacteria (clinical bacteriology)

- Analysis of water in swimming pools etc.