Before the Krebs cycle even begins, there is a process called the link reaction. This occurs when the molecule pyruvate enters the mitochondria. This pyruvate molecule would have been produced by glycolysis, where one glucose molecule goes through a series of reactions to create pyruvate. This occurs in the cytoplasm of the cell. To begin the Krebs cycle, pyruvate is decarboxylated and combined with a CoA enzyme, creating the first product required to begin the Krebs cycle. Acetyl CoA combines with oxaloacetate and begins the cycle.