The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a key metabolic pathway that generates energy through the oxidation of acetate derived from carbohydrates, fats, and proteins into carbon dioxide and water. This complex process is crucial for the production of ATP, NADH, and FADH2, which are essential for various cellular functions. The Krebs cycle takes place in the mitochondrial matrix and involves a series of chemical reactions that convert acetyl-CoA into carbon dioxide, releasing energy in the form of ATP, NADH, and FADH2.
Introduction to the Krebs Cycle
The Krebs cycle is a critical component of cellular respiration, accounting for approximately 2⁄3 of the cellular energy produced. It is a cyclic process, meaning that the last step of the cycle regenerates the first compound, allowing the cycle to continue. The Krebs cycle is named after Hans Adolf Krebs, who first described the cycle in the 1930s. The cycle involves eight distinct steps, each catalyzed by a specific enzyme, and results in the production of ATP, NADH, and FADH2 as byproducts.
Key Points
- The Krebs cycle is a key metabolic pathway that generates energy through the oxidation of acetate.
- The cycle involves eight distinct steps, each catalyzed by a specific enzyme.
- The Krebs cycle produces ATP, NADH, and FADH2 as byproducts.
- The cycle takes place in the mitochondrial matrix.
- The Krebs cycle is a critical component of cellular respiration, accounting for approximately 2/3 of the cellular energy produced.
Step 1: Citrate Synthase
The first step of the Krebs cycle involves the conversion of acetyl-CoA and oxaloacetate into citrate, catalyzed by the enzyme citrate synthase. This reaction is considered the committed step of the cycle, as it is the point of no return for the acetyl group. The citrate synthase reaction involves the condensation of acetyl-CoA and oxaloacetate, resulting in the formation of citrate and CoA.
Step 2: Aconitase
The second step of the Krebs cycle involves the conversion of citrate into isocitrate, catalyzed by the enzyme aconitase. This reaction involves the isomerization of citrate into isocitrate, which is then converted into alpha-ketoglutarate. The aconitase reaction is a critical step in the cycle, as it allows for the continued production of energy through the oxidation of alpha-ketoglutarate.
Step 3: Isocitrate Dehydrogenase
The third step of the Krebs cycle involves the conversion of isocitrate into alpha-ketoglutarate, catalyzed by the enzyme isocitrate dehydrogenase. This reaction involves the oxidation of isocitrate, resulting in the formation of alpha-ketoglutarate and CO2. The isocitrate dehydrogenase reaction is a critical step in the cycle, as it allows for the production of NADH and the continued production of energy.
Step 4: Alpha-Ketoglutarate Dehydrogenase
The fourth step of the Krebs cycle involves the conversion of alpha-ketoglutarate into succinyl-CoA, catalyzed by the enzyme alpha-ketoglutarate dehydrogenase. This reaction involves the oxidation of alpha-ketoglutarate, resulting in the formation of succinyl-CoA and CO2. The alpha-ketoglutarate dehydrogenase reaction is a critical step in the cycle, as it allows for the production of NADH and the continued production of energy.
Step 5: Succinyl-CoA Synthetase
The fifth step of the Krebs cycle involves the conversion of succinyl-CoA into succinate, catalyzed by the enzyme succinyl-CoA synthetase. This reaction involves the conversion of succinyl-CoA into succinate, resulting in the formation of GTP and CoA. The succinyl-CoA synthetase reaction is a critical step in the cycle, as it allows for the production of ATP and the continued production of energy.
| Enzyme | Reaction | Products |
|---|---|---|
| Citrate Synthase | Acetyl-CoA + Oxaloacetate → Citrate | Citrate, CoA |
| Aconitase | Citrate → Isocitrate | Isocitrate |
| Isocitrate Dehydrogenase | Isocitrate → Alpha-Ketoglutarate | Alpha-Ketoglutarate, CO2, NADH |
| Alpha-Ketoglutarate Dehydrogenase | Alpha-Ketoglutarate → Succinyl-CoA | Succinyl-CoA, CO2, NADH |
| Succinyl-CoA Synthetase | Succinyl-CoA → Succinate | Succinate, GTP, CoA |
What is the primary function of the Krebs cycle?
+The primary function of the Krebs cycle is to generate energy through the oxidation of acetate derived from carbohydrates, fats, and proteins into carbon dioxide and water.
Where does the Krebs cycle take place in the cell?
+The Krebs cycle takes place in the mitochondrial matrix.
What are the products of the Krebs cycle?
+The products of the Krebs cycle include ATP, NADH, and FADH2.
