How is DNA replicated?

Scientists have proposed several models of DNA replication but the currently accepted model is called the 'Semi-Conservative' model. The Semi-Conservative model of DNA replication was discovered by two scientists, Meselson and Stahl, through an experiment they conducted in 1958. The Semi-Conservative model relies on two major enzymes: DNA Helicase and DNA Polymerase. Firstly, DNA Helicase 'unwinds' the DNA double helix being replicated so that the two strands of DNA are separated; through this process, hydrogen bonds between bases break. Each of the two strands of DNA can now act as template strands - meaning they form the basis for a new complementary strand to be created. Next, free DNA nucleotides can begin to bind to their complementary base pairs on the template strand of DNA by hydrogen bonds,which reform. The base pairs are joined by DNA Polymerase. As a result of this joining, the original DNA molecule has been replicated - we now have two DNA molecules formed from our original one. Therefore, each new molecule of DNA contains half original DNA and half new DNA; this is why the replication is Semi-Conservative.