The Krebs cycle is a series of steps catalysed by enzymes in the matrix:
• A 2-carbon atoms Acetyl CoA enters the cycle and combines with a 4-
carbon compound (oxaloacetate) to give a 6-carbon compound
(citrate/citric acid). Coenzyme A is reformed. Cycle turns twice for each
original glucose molecule.
• The citrate is then gradually converted back to the 4-
carbon oxaloacetate again in a series of small enzyme-controlled steps
involving decarboxylation and dehydrogenation. 2 C atoms are released in 2
CO2 molecules and 4 pairs of H atoms are removed.
• The CO2 removed is given off as a waste product. It diffuses rut of the
mitochondrion and out of the cell.
• The hydrogens removed are picked up by NAD and another coenzyme
called FAD (flavin adenine dinucleotide). 1 FAD and 3 NAD molecules are
reduced during each turn of the cycle. H in reduced NAD/FAD will be released in
oxidative phosphorylation. The main role of the Krebs cycle in respiration is to
generate a pool of reduced hydrogen carriers to pass on to the next stage.
• The regenerated oxaloacetate can combine with another ACoA.
• 1 ATP is produced directly by substrate-level phosphorylation for each
ACoA entering the cycle.
• Amino acids and fatty acids can be broken down and fed into cycle.
