The citric acid cycle, also known as the Krebs cycle or tricarboxylic acid (TCA) cycle, is a series of chemical reactions that take place in the mitochondria of eukaryotic cells. It is a central metabolic pathway for the oxidation of carbohydrates, fats, and proteins to produce adenosine triphosphate (ATP), the main energy currency of cells.
The citric acid cycle starts with the entry of acetyl-CoA, which is derived from various fuel sources including glucose, fatty acids, and amino acids. Acetyl-CoA combines with a four-carbon molecule called oxaloacetate to form citrate, a six-carbon compound. Through a series of enzymatic reactions, citrate is converted back into oxaloacetate, producing NADH, FADH2, and ATP in the process.
The cycle consists of eight sequential steps, including the release of carbon dioxide and the generation of high-energy electron carriers NADH and FADH2. These carriers subsequently enter the electron transport chain, where they donate their electrons to generate a proton gradient across the inner mitochondrial membrane, leading to the synthesis of ATP through oxidative phosphorylation.
The citric acid cycle acts as a hub connecting different metabolic pathways, enabling the production of necessary energy molecules and intermediates for biosynthesis. It plays a crucial role in maintaining cellular homeostasis and is essential for various physiological processes, such as muscle contraction, brain function, and cell proliferation. Disruptions in the citric acid cycle can lead to metabolic disorders and dysfunction of cellular energy production.
