Practice question

Despite double-stranded DNA chemically offering two complementary sequences, transcription uses only one as template to avoid production of overlapping complementary RNAs that would anneal into inert duplex. Within transcription bubble, polymerase binds template strand oriented 3' to 5' to synthesize RNA antiparallel, while coding non-template strand displaced. Template strand determination defined by promoter orientation and direction of polymerase binding. Only antisense strand read, also called template or transcribed strand, ensures mRNA sequence uniqueness. Using single strand prevents simultaneous transcription interference and maintains directional control of gene expression at each locus.