transcription

Transcription is like photocopying a single page from a vast reference book so you can carry it out of the library. The cell keeps its master DNA safe in the nucleus but copies an individual gene into a portable RNA message that can travel to where proteins are made.

An enzyme reads one strand of the gene's DNA — the template strand — and stitches together a complementary RNA strand following base-pairing rules, except that RNA uses uracil (U) wherever DNA would use thymine (T). The RNA copy reproduces the gene's information without disturbing the original DNA.

Transcription is the first and most heavily controlled step of gene expression: cells decide which genes to transcribe, when, and how much, allowing the same genome to run a nerve cell or a skin cell. In eukaryotes the raw RNA is then processed — capped, spliced, and tailed — before it is ready to be read.