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How is DNA transcribed into messenger RNA?

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Diagram of a DNA polynucleotide chain showing linked deoxyribose sugars, phosphate groups, and nitrogenous bases (adenine, guanine, cytosine, thymine), with an inset comparing ribose and uracil in RNA. — Nucleic acid A portion of the polynucleotide chain of deoxyribonucleic acid (DNA), with an inset showing the corresponding pentose sugar and pyrimidine base in ribonucleic acid (RNA).

Transcription is the biological process by which the genetic information in DNA is copied into messenger RNA (mRNA). This process is catalyzed by the enzyme RNA polymerase and occurs in several key steps.123

The Process of Transcription

Initiation: RNA polymerase recognizes and binds to a specific DNA sequence called a promoter, which marks the start of a gene. At this site, the two strands of the DNA double helix separate.23
Elongation: Using one DNA strand as a template, RNA polymerase synthesizes a complementary RNA chain. It incorporates ribonucleoside monophosphates by cleaving high-energy phosphate bonds from ribonucleoside triphosphates.23
Base Pairing: The sequence of the RNA is determined by complementary base pairing rules: cytosine (C) in DNA pairs with guanine (G) in RNA, G pairs with C, thymine (T) pairs with adenine (A), and adenine (A) pairs with uracil (U).23
Termination: Once a termination signal is reached, the RNA polymerase releases the DNA, and the newly formed RNA molecule is detached.23

In eukaryotes, the initial product is a pre-mRNA that undergoes extensive processing, such as splicing, before becoming mature mRNA.23