 Okay, we turn now to the Krebs cycle which happens in the middle of the mitochondria if there's oxygen present. If so, pyruvate molecules are moved from the cytosol into the mitochondria and are converted into something called acetyl-coenzyme A, which is another molecule which is needed to kickstart the Krebs cycle. In this phase, some common oxide is also produced. The Krebs cycle is another eight steps of conversions by eight different specific enzymes. Some more electron transfer happens in the Krebs cycle. Electrons are added to NAD+, to get NADH, and a similar molecule called FAD also takes on electrons to become FADH2. So in the Krebs cycle, for one molecule of glucose that started out in glycolysis, we end up with another two molecules of ATP, so that's four we've now got. We have another eight molecules of NADH and two molecules of FADH. We also have six molecules of carbon dioxide.