TCA Cycle (Citric acid cycle or Krebs cycle)


The TCA cycle, also known as the citric acid cycle or the Krebs cycle, is a series of biochemical reactions that take place in the mitochondria of eukaryotic cells and in the cytoplasm of prokaryotic cells. The TCA cycle is a key metabolic pathway that connects carbohydrate, fat, and protein metabolism. The main function of the TCA cycle is to oxidize acetyl-CoA, a two-carbon molecule derived from the breakdown of glucose, fatty acids, and amino acids, to carbon dioxide and water, while generating high-energy molecules such as NADH and FADH2. These molecules then donate their electrons to the electron transport chain, which drives the synthesis of ATP, the universal energy currency of the cell.

The TCA cycle was discovered by Hans Krebs in 1937, who received the Nobel Prize in Physiology or Medicine in 1953 for his work. The cycle is named after citric acid, the first molecule formed in the cycle by the condensation of acetyl-CoA and oxaloacetate. The cycle consists of eight enzymatic steps that regenerate oxaloacetate at the end, allowing the cycle to continue. The TCA cycle is also involved in various biosynthetic pathways, as some of its intermediates serve as precursors for other molecules such as amino acids, nucleotides, and heme.

The TCA cycle is a central metabolic pathway that plays a vital role in cellular respiration and energy production. It is also a source of diversity and complexity in metabolism, as it links different macromolecules and provides building blocks for various biosynthetic processes. Understanding the TCA cycle is essential for comprehending how cells utilize nutrients and generate energy under different physiological conditions.