DNA+Replication

__DNA REPLICATION__
by Denisse SImonian First, we have the normal, double helix DNA strand. Then, the protein, helicase comes in and breaks the hydrogen bonds between the bases. So it forms 2 strands which look like a Y. The place where the splitting starts is the Replication Fork, or the y-fork. After the double strand has been split, binding proteins called Single-Stranded DNA Binding proteins come and attach themselves to the separated DNA strands. Without these, the strands could reattach and form the double helix again. DNA Polymerase then comes along and attaches itself to one strand. As it moves along the strand, it joins nucleotides together, forming a new strand. Because this new strand is continuous, it is called the Leading strand. On the second strand, the nucleotides attach uncontinuously. So this strand is called the Lagging strand. For replication to begin on the lagging strand, RNA primase comes and makes RNA primers. A different DNA polymerase then comes along and joins the nucleotides. But, this DNA polymerase makes shorter dicontinuous strands and it stops when it meets another RNA primer. The polymerase goes back up to another newly formed RNA primer and starts to make nucleotides again. Then, the enzyme RNAse H removes the RNA primers on the lagging strand. This leaves small gaps on what should be the newly formed strand. Because of the gaps, the strand is not continuous and is in fragments. These fragments are called Okazaki Fragments. DNA Ligase comes and stiches up the short gaps between the Okazaki fragments. This forms the new completed lagging strand. The replication process is complete and we now have 2 new double stranded DNA.