And nucleotide bases are used to form DNA molecules, RNA molecules that are used to form ACP, the energy currency of the cell. So amino acids are very important molecules, and we also actually utilize amino acids for energy, as we'll see in electra to come. Now, what exactly are the sources of amino acids? Well, ten out of the 20 amino acids used by the cells of our body are actually synthesized inside our cells. So we can synthesize amino acids, ten amino acids from scratch, but the other ten amino acids are called essential amino acids. And that's because we cannot actually synthesize those ten amino acids.