So although single stranded DNA molecules work, double stranded DNA molecules are more effective and more common as templates. So RNA polymerase uses this DNA template to basically build a polynucleotide chain that contains complementary bases as we'll see in just a moment. And finally, inside the RNA polymerase molecule at the center there is a pocket that can fit a divalent metal atom. Now, what is a divalent metal atom? Well, it's a metal atom that can gain a positive charge, a charge of positive two. So he can lose two electrons and gain a positive charge of two.