Cytosine-guanine interaction. Computer artwork showing the structure of bound cytosine (left) and guanine molecules (right). Atoms are shown as colour-coded spheres: carbon (green), hydrogen (white), nitrogen (blue) and oxygen (red), with the bonds between them as rods. Cytosine and guanine are two of the bases found in DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). The positioning of these bases along the RNA and DNA chains is known as the genetic code. Each genetic code is unique and gives organisms their individual characteristics. In DNA and RNA cytosine always pairs up with guanine.