Metabolic Pathways

Primary Metabolic Pathways

• Catabolism

• Energy-generating metabolism

• Degradation mechanism

• Anabolism

• Energy utilizing pathway

• Biosynthetic

Catabolic Pathways

• Breakdown metabolism

• Substrate-level phosphorylation

• Products:

• ATP

• NADH

• NADPH

• FADH2

• heat

Embden-Meyerhoff-

Parnas Pathway

• Most common route

• Aerobic and anaerobic conditions

• Three key regulatory enzymes

Pentose Phosphate

(PP) Pathway

• Hexose Monophosphate Pathway

• Operates with EMP pathway

• Aerobic or anaerobic conditions

• Catabolic and anabolic roles

Entner–Doudoroff

(ED) pathway

• Used by few microbes lacking EMP

pathway

• G(-) bacteria

• Azotobacter, Pseudomonas, Rhizobium,

Xanthomonas and Zymomonas

Phosphoketolase (PK)

pathway

• Warburg–Dickens pathway

• Lactic acid bacteria (LAB)

• Heterolactic fermentation

Tricarboxylic acid

cycle (TCA)

• Aerobic conditions

• Further catabolism of pyruvate

Respiration

• Aerobic respiration

• Oxidative phosphorylation

• Chemiosmotic hypothesis

• Anaerobic respiration

• ETS as with aerobic respiration

Anaerobic Respiration

• Nitrate respiration

• Facultative anaerobes

• Redox potential:

• +0.42 : nitrate

• +0.82: oxygen

• Denitrification

• Nitrate → nitrite → nitrous oxide

• Pseudomonas, Paracoccus denitrificans and Thiobacillus denitrificans

Anaerobic Respiration

• Sulfate respiration

• Obligate anaerobes (Desulfovibrio sp.)

• Main product: H2S

• Carbonate respiration

• Archeans (Methanococcus and Methanobacterium)

• CO2+4H2→CH4+2H2O

Fermentation

Fermentation

Fermentation