Metabolism II: Fate of Pyruvate

NAD+

  • Glycolysis reduces NAD+ to NADH and H+
  • Only limited amounts of NAD+ are present in a cell - NADH must be regenerated through the oxidative metabolism of pyruvate

TCA cycle

  1. Pyruvate enters mitochondrial matrix
    1. H+/pyruvate symport by facilitated diffusion
  1. Pyruvate is converted into acetyl-CoA
    1. Catalysed by PDC
    2. Allosterically regulated by phosphorylation
notion image
  1. C2 (acetyl-CoA) condenses with C4 (oxeloacetate) → C6 (citrate)
  1. C6 is decarboxylated twice, yielding 2x CO2
  1. Four oxidation reactions yield NADH+, H+ and FADH2
  1. One GTP formed
  1. C4 recreated
 
All enzymes of the TCA cycle are located in the matrix, apart from succinate dehydrogenase which is integrated into the inner mitochondrial membrane

Products of the TCA cycle

  • 3 pairs of electrons transferred in the conversion of NAD+ to NADH and H+
  • 1 pair of electrons needed to reduce FAD to FADH2
From each acetyl-CoA, TCA cycle generates:
  • 3 NADH + H+
  • 1 FADH2
  • 1 GTP
  • 2 CO2