The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a central metabolic pathway in cellular respiration. It plays a crucial role in energy production by oxidizing acetyl-CoA derived from carbohydrates, fats, and proteins into carbon dioxide (CO₂) and high-energy molecules such as NADH and FADH₂. This process occurs in the mitochondrial matrix of eukaryotic cells and the cytoplasm of prokaryotic cells.
Overview
- Location: Mitochondrial matrix (eukaryotes) and cytoplasm (prokaryotes).
- Function: Oxidation of acetyl-CoA to produce ATP, NADH, FADH₂, and CO₂.
- Importance: Serves as a hub for metabolism, connecting carbohydrate, fat, and protein catabolism.
Steps of the Krebs Cycle
The cycle consists of eight enzymatic steps:
- Formation of Citrate: Acetyl-CoA (2 carbons) combines with oxaloacetate (4 carbons) to form citrate (6 carbons), catalyzed by citrate synthase.
- Isomerization: Citrate is converted into isocitrate by aconitase.
- Decarboxylation: Isocitrate is oxidized to α-ketoglutarate (5 carbons), releasing CO₂ and reducing NAD⁺ to NADH.
- Second Decarboxylation: α-ketoglutarate is converted to succinyl-CoA (4 carbons), releasing another CO₂ and producing NADH.
- ATP/GTP Formation: Succinyl-CoA is converted to succinate, generating one ATP or GTP via substrate-level phosphorylation.
- Oxidation: Succinate is oxidized to fumarate, producing FADH₂.
- Hydration: Fumarate undergoes hydration to form malate.
- Regeneration of Oxaloacetate: Malate is oxidized back to oxaloacetate, producing NADH.
