And if that hydroxyl group is not present, as in this case, it will not be able to form that phospholdiaester bond. And so DNA replication would essentially stop. And so what this DD NTP molecule is used for in this method is to basically stop the process of DNA replication. And we'll see why that's important towards the end of this lecture. So let's move on to these four steps. So, in step one of the standard DNA sequencing, we have to actually obtain that DNA molecule that we want to sequence.