Pyruvate is a byproduct of glycolysis that is transformed into acetyl CoA, which enters the Krebs cycle when enough oxygen is available.
Pyruvate is created in the cytoplasm and transferred to the mitochondria, where it is transformed to acetyl-CoA; acetyl-CoA then interacts with oxaloacetate to make citrate, entering the tricarboxylic acid (TCA) cycle.
Pyruvate enters the mitochondria and undergoes oxidative decarboxylation to create acetyl CoA, which enters the Krebs cycle.