Whats happens to the dna molecule at the beginning of transcription

Rna polymerase binds to a dna molecule and seperates its 2 strands

Dna uzips in the nucleus bond together and form a complementary strand of mRNA codons using the sequence of nucleotides on the DNA strand as a template (pattern). This strand of mRNA exits the nucleus to transfer this pattern to the ribosome where it is interpreted and used to assemble a protein.