1. The Krebs Cycle By Stephanie Worrall

2. The Krebs Cycle Discovered by biochemist Sir Hans Krebs In the year 1937 Is responsible for the breakdown of pyruvate Acts as a central metabolic pathway in the breakdown of foods Alternative names; The citric acid cycle and Tricarboxylic acid cycle Occurs in the mitochondrial matrix

3. Definition of the Krebs cycle A series of enzyme catalysed reactions that oxidise the acetyl group of acetyl CoA to 2 molecules of Carbon dioxide. It also produces 1 molecule of ATP by substrate level phosphorylation, and reduces 3 molecules of NAD and one molecule of FAD.

4. 1.Cycle begins with the 2C acetyl group (acetate) attached to Coenzyme A, which combines with Oxaloacetate (4C compound) 2.Citrate (6C compound) is produced from the combining of oxaloacetate and acetate 3.Citrate is decarboxylated and dehydrogenated to form a 5 carbon compound. NAD is reduced by the pair of hydrogen atoms 4.The 5 carbon compound is then decarboxylated and dehydrogenated to form a 4 carbon compound and a molecule of reduced NAD

5. 5.4 carbon compound is changed into another 4 carbon compound 6.ADP is phosphorylated to produce a molecule of ATP 7.The second 4 carbon compound is changed into another 4 carbon compound 8.Coenzyme FAD is reduced – due to accepting a pair of hydrogen atoms that have been removed 9.The resulting 4-carbon compound (from 7.) is dehydrogenated, which regenerated oxaloacetate 10.A molecule of NAD is reduced

6. Substrate- level phosphorylation The formation of ATP from ADP and Pᵢ

7. Citrate (6C) in converted back to oxaloacetate, involving 2 types of reactions: Decarboxylation Reactions – Carbon atoms are removed from the Krebs cycle intermediate compounds forming CO 2 (Catalysed by decarboxylase enzymes) Dehydrogenation Reactions – Intermediate compounds are oxidised by the removal of hydrogen atoms,hydrogen atoms are taken up by hydrogen acceptor molecules e.g. NAD and another molecule FAD. (catalysed by dehydrogenase enzymes) Reduced NAD and Reduced FAD are oxidised in the electron transport chain: yielding energy to generate ATP from ADP One molecule of ATP is directly synthesised in the Krebs Cycle The Krebs cycle has to turn twice for each glucose oxidised ( as 2 molecules of pyruvate are produced from each glucose )

8. Summary Acetate(2C) Combines with Oxaloacetate(4C) to form Citrate (6C) Citrate (6C) undergoes a series of reactions, eventually losing 2 Carbon atoms, regenerating the 4 carbon compound (oxaloacetate) The 2 carbon atoms are lost as CO 2 The 6C compound (citrate) is oxidised by the removal of H atoms The H atoms pass to hydrogen acceptor molecules, 3 molecules of reduced NAD and One of FAD are formed

9. Products 6 Reduced NAD 2 Reduced FAD 4 CO 2 2 ATP