What are the main steps in …

The TCA cycle takes place over eight different steps: Step 1: First the acetyl CoA (a two carbon molecule) joins with oxaloacetate (4 carbon molecule) to form citrate (6 carbon molecule). Step 2: The citrate is then converted to isocitrate (isomer of citrate) Step 3: Isocitrate is then oxidised to alpha-ketoglutarate (a five carbon molecule) which results in the release of carbon dioxide. One NADH molecule is also formed in this step. The enzyme responsible for catalysing this step is isocitrate dehydrogenase. This is a rate limiting step as isocitrate dehydrogenase is an allosterically controlled enzyme. Step 4: Here alpha-ketoglutarate is oxidised to form a 4 carbon molecule which picks up coenzyme A forming succinyl CoA. This conversion also forms a NADH molecule. Step 5: Succinyl CoA is then converted to succinate (4 carbon molecule) and one GTP molecule is produced. Step 6: Succinate is converted into fumarate (4 carbon molecule) and a molecule of FADH₂ is produced. Step 7: Fumarate is converted to malate (another 4 carbon molecule). Step 8: Malate is then converted into oxaloacetate and NADH is also produced here.