Kreb's cycle or TCA cycle consists of two successive steps of decarboxylation, leading to the formation of α-ketoglutaric acid and then succinyl-CoA. In the remaining steps of citric acid cycle, succinyl-CoA is oxidised to OAA allowing the cycle to continue. During the conversion of succinyl-CoA to succinic acid a molecule of GTP is synthesised. This is a substrate level phosphorylation.
Conversion of pyruvate to acetyl CoA belongs to oxidative decarboxylation. This acetyl CoA enters the Kreb's cycle.
Passing on of the electrons removed as part of the hydrogen atoms to molecular O2 with simultaneous synthesis of ATP is the second curial event of aerobic respiration which is a part of electron transport system.