Q: Outline the main features of a Krebs cycle

The Krebs cycle occurs in the matrix of the mitochondrion. It occurs only in aerobic conditions, that is, only when oxygen is present. Its main function is to oxidise acetyl CoA generated from glycolysis. In the Krebs cycle, acetyl CoA and oxaloacetate undergo a condensation reaction to form a six-carbon compound. Through a series of decarboxylation and dehydrogenation reactions, intermediate 5-carbon and 4-carbon compounds are formed with the release of carbon dioxide. 1 ATP molecule is generated per turn of the Krebs cycle by substrate level phosphorylation; hence 2 ATP molecules are formed per molecule of glucose. Most fo the chemical energy is transferred during the redox reactions where the electron carriers NAD and FAD are reduced to form coenzymes NADH and FADH2, respectively. The Krebs cycle is also cyclic as the starting product, oxaloacetate, is regenerated.