During transcription, the enzyme RNA polymerase uses one strand of DNA as a template to assemble complementary nucleotides into a strand of RNA.
The figure has following structures Nucleus.
RNA polymerase.
Adenine (DNA and RNA) represented by green.
Cytosine (DNA and RNA) represented by purple.
Guanine (DNA and RNA) represented by red.
Thymine (DNA only) represented by yellow.
Uracil (RNA only) represented by orange.