What is Krebs Cycle ?

Krebs Cycle      As implied by cycle the Krebs cycle is not a linear series of reactions with a start and end point but a closed circle of reactions with no beginning or end point. Pyruvate is produced by glycolysis in the cytoplasm and enters the matrix of the mitochondrion. Pyruvate does not enter the cycle directly but indirectly by means of a linking step that converts pyruvate into acetyl-CoA with the production of CO2 and NADH  +  H+.     Each molecule of glucose produces 2 pyruvates which by means of the linking reaction yields 2 acetyl-CoA that enter the Krebs cycle. As a result of the linking step and the Krebs cycle each molecule of glucose produces: 1. 6 CO2 molecules (each pyruvate produces one CO2 in the linking step and two CO2 in the cycle); 2. 2 ATP's directly (one for each acetyl-CoA that enters the cycle); 3. Ten reduced coenzymes (each pyruvate reduces one NAD+ in the linking step, and each acetyl-CoA reduces 3 NAD+ and one FAD in each turn of the cycle).      The overall reaction from pyruvate to the Krebs cycle is then: 2pyruvate + 8NAD+ + 2FAD + 2ADP + 2Pi + 6H2O ® 6CO2 + 8NADH + 8H+ + 2FADH2 + 2ATP      When combined with glycolysis the oxidation of glucose yields 4 ATP's (2 from glycolysis and 2 from Krebs citric acid cycle) and 12 reduced coenzymes (2 NADH from glycolysis and 10 reduced coenzymes from the Krebs cycle including the linking reaction).      All the CO2 that will be produced is produced during the Krebs cycle and the linking step. No O2 is consumed. Oxygen consumption occurs in the next stage oxidative phosphorylation.