The Krebs Cycle (Citric Acid Cycle) By Zuzana Kollarova

Krebs Cycle  Enzymes in the matrix of the mitochondria catalyze a cycle of reactions called the Krebs cycle.  The common pathway to completely oxidize fuel molecules which mostly is acetyl CoA,the product from the oxidative decarboxylation of pyruvate  It enters the cycle and passes ten steps of reactions that yield energy and CO2  These reactions can only occur if oxygen is available and so are part aerobic cell respiration  Prokaryotic cells – occurs in the cytoplasm  Eukaryotic cells – occurs in the mitochondria

Steps: 1. In the first reaction of the cycle an acetyl group is transferred from acetyl CoA to a four-carbon compound (oxyloacetate) to form a six-carbon compound (Citrate). 2. Citrate is converted to isocitrate. 3. The 6-carbon isocitrate is oxidized by NAD+ to produce reduced NADH and 5-carbon alpha- ketoglutarate. One carbon is lost as CO2 (decarboxylation). CO2 is waste product. 4. The 5-carbon alpha-ketoglutarate is oxidized by NAD+ to produce reduced NADH and 4-carbon succinyl-CoA. (One carbon is lost as CO2.)

5. Hydrogen is removed – Oxidation of succinyl-CoA produces succinate and one GTP that is converted to ATP. Oxidation reactions release energy, much of which is stored by the carriers when they accept hydrogen. 6. Oxidation of succinate by FAD produces reduced FADH2 and fumarate. 7. Fumarate is converted into malate 8. Oxidation of malate by NAD+ produces reduced NADH and oxaloacetate

 Animation: 3X7KQ 3X7KQ 3X7KQ