STPM Biology - chapter 5 (old syllabus) chapter 5 (new syllabus): Revision essay question 5

5. Describe Kebs cycle showing how NADH,FADH₂,GTP are produced and the release of carbon dioxide.

Answer

Pyruvate is converted to acetyl coenzyme A by the removal of CO₂ and reduction of NAD to NADH.Acetyl CoA combines with oxaloacetate to form citrate and coenzyme A is released.

Citrate rearranges to form its isomer isocitrate that is later converted to oxalosuccinate,NAD is reduced to NADH.Oxalosuccinate is decarboxylated to α-ketoglutarate.

Oxidative-decarboxylation of α-ketoglutarate produces succinat, 1 molecule CO₂ is released, 1 molecule of NADH and 1 molecule GTP are formed via substrate level phosphorylation.The phosphate group from GTP is transferred to ADP forming ATP.Succinate is converted to fumarate,FAD becomes hydrated and is converted to malate.NAD is reduced to NADH.Malate is oxidized to oxaloacetate.

Oxaloacetate that has been regenerated can combine with acetyl CoA again,and the cycle is repeated.For every acetyl CoA again,and the cycle is repeated.For every acetyl CoA that enters the Krebs cycle,3 molecule of NADH,1 FADH molecule and 1 ATP molecule are produced.