[PSM] TCA Cycle and Fermentation

Acetyl-CoA + Oxaloacetate → Citrate

Reaction: Citrate Synthase

Citrate → Isocitrate

Reaction: Aconitase

Isocitrate → alpha-Ketoglutarate + CO₂ + NADH

Reaction: Isocitrate dehydrogenase

Isocitrate Dehydrogenase

Enzyme: Isocitrate → alpha-Ketoglutarate + CO₂ + NADH

alpha-Ketoglutarate + CO₂ → Succinyl-CoA + CO₂ + NADH

Reaction: Alpha-Ketoglutarate Dehydrogenase

Alpha-Ketoglutarate Dehydrogenase

Enzyme: alpha-Ketoglutarate + CO₂ → Succinyl-CoA + CO₂ + NADH

Succinyl-CoA → Succinate + GTP

Reaction: Succinyl-CoA synthetase

Succinyl-CoA synthetase

Enzyme: Succinyl-CoA → Succinate + GTP

Succinate → Fumarate + FADH2

Reaction: Succinate dehydrogenase

Succinate dehydrogenase

Enzyme: Succinate → Fumarate + FADH2

Fumarate → Malate

Reaction: Fumarase

Fumarase

Fumarate → Malate

Malate → Oxaloacetate + NADH

Reaction: Malate dehydrogenase

Malate dehydrogenase

Enzyme: Malate → Oxaloacetate + NADH

3 NADH, 1 FADH2, 1 GTP/ATP, 2 CO2

What is the net yield per Acetyl-CoA that enters TCA?

Isocitrate → Alpha-ketoglutarate + NADH + CO2 (isocitrate dehydrogenase)

Rate limiting step of TCA

Cytoplasm for prokaryotes
Mitochondria for eukaryotes

TCA cycle occurs in which cell parts?

Succinate dehydrogenase

Enzyme that produces FADH2

Succinyl-CoA synthetase

Enzyme that produces GTP or ATP

Lactic Acid Fermentation

Anaerobic process that regenerates NAD⁺ from NADH, allowing glycolysis to continue.

Pyruvate → Lactate + NAD+ (Pyruvate reductase / Lactate dehydrogenase)

Summary of Lactic Acid Fermentation

2 ATP (from glycolysis), 2 Lactate, NAD_

Net result per glucose for lactic acid fermentation

Leuconostoc

Bacteria that can produce both lactic acid and ethanol

Ethanol (Alcoholic) Fermentation

Anaerobic process converting pyruvate to ethanol + CO₂, regenerating NAD⁺

Pyruvate → Acetaldehyde + CO2 (pyruvate decarboxylase)

Step 1 in ethanolic fermentation

Acetaldehyde → Ethanol + NAD+ (alcohol dehydrogenase)

Step 2 in ethanolic fermentation

2 ATP (from glycolysis), 2 Ethanol, 2 CO2, NAD+

Net result per glucose in ethanolic fermentation

Zymomonas mobilis

Microorganism that uses Entner-Doudoroff (instead of glycolysis) pathway prior to ethanol fermentation