DNA template (3'?5')DNA coding (5'?3')mRNA transcriptRNA polymerase (transparent)
What is transcription?
RNA polymerase (RNAP) attaches to the DNA and unwinds the double helix, creating a transcription bubble. It reads the template strand (3'?5') and builds a complementary mRNA strand (5'?3'). In RNA, Uracil (U) replaces Thymine (T) — so A on DNA becomes U on mRNA. The RNAP is shown transparent so you can see the bases being read underneath. Once complete, the mRNA travels out of the nucleus to the ribosome.
The ribosome assembles around the mRNA and slides along it one codon (3 bases) at a time. Each codon is recognised by a matching tRNA anticodon carrying a specific amino acid. The ribosome catalyses a peptide bond between each new amino acid and the growing chain. When a stop codon (UAA, UAG or UGA) enters the ribosome, no tRNA matches — a release factor binds instead, and the finished polypeptide is released. The polypeptide then folds into a functional protein.