The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid cycle (TCA cycle), is a complex series of chemical reactions that take place in the mitochondria of eukaryotic cells. It is named after Sir Hans Adolf Krebs, a German-British biochemist who first elucidated the cycle in 1937. The Krebs cycle is a vital metabolic pathway that produces ATP, the energy currency of the cell, by breaking down carbohydrates, fats, and proteins.
The Krebs cycle starts with acetyl-CoA, a molecule that is formed from the breakdown of carbohydrates, fats, and proteins. Acetyl-CoA enters the cycle by combining with a four-carbon molecule called oxaloacetate, which forms a six-carbon molecule called citrate. The citrate then undergoes a series of reactions that release two molecules of CO2, producing a four-carbon molecule called oxaloacetate, which can combine with another molecule of acetyl-CoA to start the cycle again.
the Krebs Cycle Processes
The Krebs cycle is a series of eight chemical reactions, each catalyzed by a specific enzyme. Let’s take a closer look at each step of the cycle:
- Citrate Synthase: The first step in the cycle is the condensation of acetyl-CoA and oxaloacetate to form citrate. This reaction is catalyzed by citrate synthase.
- Aconitase: Citrate is then converted into isocitrate in a reaction catalyzed by aconitase.
- Isocitrate Dehydrogenase: Isocitrate is then oxidized to form alpha-ketoglutarate in a reaction catalyzed by isocitrate dehydrogenase. This reaction also releases a molecule of CO2 and produces NADH, a molecule that carries electrons to the electron transport chain.
- Alpha-ketoglutarate Dehydrogenase: Alpha-ketoglutarate is then oxidized to form succinyl-CoA in a reaction catalyzed by alpha-ketoglutarate dehydrogenase. This reaction also releases a molecule of CO2 and produces NADH.
- Succinyl-CoA Synthetase: Succinyl-CoA is then converted into succinate in a reaction catalyzed by succinyl-CoA synthetase. This reaction also produces a molecule of GTP, a molecule that can be used to generate ATP.
- Succinate Dehydrogenase: Succinate is then oxidized to form fumarate in a reaction catalyzed by succinate dehydrogenase. This reaction also produces FADH2, another molecule that carries electrons to the electron transport chain.
- Fumarase: Fumarate is then converted into malate in a reaction catalyzed by fumarase.
- Malate Dehydrogenase: Malate is then oxidized to form oxaloacetate in a reaction catalyzed by malate dehydrogenase. This reaction also produces NADH.
Summary Of The Krebs Cycle
Overall, the Krebs cycle produces two molecules of ATP, eight molecules of NADH, and two molecules of FADH2 per cycle. These electron carriers then enter the electron transport chain, which produces a large amount of ATP through oxidative phosphorylation.
The Krebs cycle is a central metabolic pathway that is essential for energy production in eukaryotic cells. It plays a critical role in breaking down carbohydrates, fats, and proteins, and it produces ATP, which is necessary for the functioning of the cell. The cycle is tightly regulated by a variety of factors, including the availability of substrates, the activity of enzymes, and the presence of feedback inhibitors