The Krebs cycle (alias, the citric acid cycle, alias the tricarboxylic acid cycle), when reduced to its most fundamental purpose, generates reducing power in the form of NADH and FADH2. It does this by “dissecting off” hydrogens from two carbon fragments remaining after glucose goes through glycolysis and subsequent decarboxylation of pyryvate yielding acetyl coenzyme A. The acetyl group is fed into the cycle by attachment to oxaloacetate, yielding citrate.
Here is an overview of the molecules involved in the Krebs cycle
What follows are molecular models of the sequential molecules involved in the Krebs Cycle: