Now, number two, it actually needs a preexisting DNA template molecule. So usually we're dealing with a double stranded DNA molecule and a double stranded DNA molecule works the best. But in some cases we can also use single stranded DNA molecules as templates. Now, why do we need a template molecule? Well, we need the DNA template to basically copy that genetic information. And it's the template, that DNA template that is used to basically bring those complementary bases to that elongated polynucleotide chain.