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RNA polymerase attaches to the DNA	RNA polymerase attaches to the DNA double-helix at the beginning of a gene. The hydrogen bonds between the two DNA strands in the gene break, separating the strands, and the DNA molecule uncoils at that point, exposing some of the bases. One of the strands is then used a a template to make an mRNA copy.
Complementary mRNA is formed	The RNA polymerase lines up free RNA nucleotides alongside the exposed bases on the template strand. The free base are attracted to their exposed bases. Specific, complementary base paring means that the mRNA strand is a complementary copy of the DNA template strand. Once the RNA nucleotides have paired up with their specific bases on the DNA strand, they're joined together by RNA polymerase, forming an mRNA molecule.
RNA polymerase moves down the DNA strand	The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand. The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double-helix
RNA polymerase reaches stop signal	When RNA polymerase reaches a particular sequence od DNA called a stop signal, it stops making mRNA and detaches from the DNA. In eukaryotes mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm.

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