So the citric acid cycle is a very important cycle. It's the center of aerobic cellular respiration, of glucose metabolism. So the citric acid cycle functions to provide a means by which any fuel molecule so what is a fuel molecule? Well, a fuel molecule is a molecule that contains carbon atoms and can be oxidized to obtain these electrons, which then can be used, as we'll see, in just a moment, to form ATP molecules. Now, the citric acid cycle also functions to provide the building blocks needed to form biological molecules such as nucleotide bases, amino acids, glucose molecules, porphyrin molecules and so forth. And we'll discuss all this in much more detail in lectures to come.