And number four, we actually need the four different types of deoxyribonucleocide triphosphate. So remember, we have adenine, guanine, we also have cytosine and thymine. We need these four ingredients to actually produce that sequence of DNA that we want to amplify. So these are the four main ingredients. Now, the next question is what exactly are the steps and how many steps are there within a single cycle of PCR? So basically, if we take a single PCR cycle, we can break that cycle down into three different steps.