Transcription (biology)
Transcription is the first step of gene expression in which a specific segment of DNA is copied into RNA (messenger RNA, mRNA) by the enzyme RNA polymerase. The process occurs in the nucleus of eukaryotes and the cytoplasm of prokaryotes, and involves three stages: initiation at the promoter, elongation of the RNA strand, and termination at a specific sequence. The resulting pre-mRNA in eukaryotes undergoes processing (5' capping, polyadenylation, and splicing) before being exported to the cytoplasm for translation.
Stages of Transcription in Eukaryotes
| Stage | Key Event | Key Proteins | Location |
|---|---|---|---|
| Initiation | RNA polymerase binds promoter | Transcription factors, RNA Pol II | Promoter region |
| Promoter clearance | RNA Pol escapes the promoter | TFIIH, RNA Pol II | Promoter/template |
| Elongation | RNA strand synthesized 5' to 3' | RNA Polymerase II | Template strand |
| Termination | RNA Pol dissociates at terminator | Cleavage factors, Poly-A polymerase | Termination signal |
| Processing | 5' cap and poly-A tail added; introns spliced | Spliceosome, capping enzymes | Nucleus |
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Related Terms
Translation (biology)
Translation is the process by which a ribosome decodes the nucleotide sequence of a messenger RNA (mRNA) and synthesizes the corresponding sequence of amino acids to produce a polypeptide chain. It occurs in three phases — initiation, elongation, and termination — and takes place at ribosomes in the cytoplasm of both prokaryotes and eukaryotes. The genetic code, read in triplets called codons, determines which amino acid is incorporated at each step, with transfer RNA (tRNA) molecules acting as adaptors between the mRNA codons and the amino acids.
Messenger RNA (mRNA)
Messenger RNA (mRNA) is a single-stranded RNA molecule that carries genetic information transcribed from DNA and serves as the template for protein synthesis during translation. In eukaryotes, the primary transcript (pre-mRNA) is processed in the nucleus by addition of a 5' 7-methylguanosine cap, a 3' poly-adenylate tail, and removal of non-coding introns by the spliceosome before being exported to the cytoplasm. The lifespan of an mRNA molecule varies from minutes to hours and is tightly regulated, making mRNA abundance a key determinant of gene expression levels.
Promoter (genetics)
A promoter is a regulatory DNA sequence located upstream (5') of a gene's transcription start site (+1) to which RNA polymerase and transcription factors bind to initiate transcription. In prokaryotes, the consensus promoter elements include the −10 (Pribnow box: TATAAT) and −35 (TTGACA) sequences; in eukaryotes, the core promoter often contains a TATA box (~−30), an initiator element (Inr) at +1, and downstream promoter elements (DPE). The strength of a promoter — determined by how closely its sequence matches the consensus — directly controls the frequency of transcription initiation and therefore the level of gene expression.
From Latin transcribere, meaning "to copy" or "to write over." The term was adopted in molecular biology in the 1950s–60s to describe copying genetic information from DNA into RNA, drawing an analogy to transcribing written text.