Transcription
Molecular Biology · Genetics · Biochemistry
Say it: tran-SKRIP-shun
Transcription is the process in which a cell copies the DNA sequence of a gene into a matching strand of RNA.
Definition
What is transcription?
Transcription is the first step of gene expression. An enzyme called RNA polymerase reads one strand of a gene, the template strand, and builds a complementary RNA molecule. The new RNA matches the other DNA strand, the coding strand, except that it carries uracil (U) wherever DNA has thymine (T). RNA is always built in the 5' to 3' direction, and unlike DNA polymerase, RNA polymerase needs no primer to start.
The process has three stages. In initiation, RNA polymerase binds a promoter, a stretch of DNA just upstream of the gene; bacteria use a sigma factor to find promoters, while eukaryotes need several transcription factors, often assembled at a TATA box. In elongation, the enzyme opens a small bubble of DNA and adds matching RNA nucleotides. In termination, a signal in the sequence makes it release the finished RNA.
In bacteria, ribosomes can begin translating an RNA while it is still being made. In eukaryotes, transcription takes place in the nucleus, and the first product, pre-mRNA, is capped, given a poly-A tail and spliced before export. RNA polymerase II makes the messenger RNA of protein-coding genes.
Word parts
Where does the word “transcription” come from?
- trans-
- across, overLatin trans
- script-
- writtenLatin scribere, to write
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Terms that go with it
- Messenger RNAMessenger RNA is the RNA copy of a gene that carries protein-building instructions from DNA to the ribosomes, where it is read in three-base codons.
- RNARNA is a usually single-stranded nucleic acid, built with the sugar ribose and the base uracil, that carries and uses genetic information to make proteins.
- Gene expressionGene expression is the use of a gene's information to make a working product, usually a protein or a functional RNA molecule.
- RNA splicingRNA splicing is the step in which introns are cut out of a newly made RNA and its exons are joined, producing a mature RNA ready for use.
- TranslationTranslation is the process in which a ribosome reads the codons of a messenger RNA and links amino acids in that order to build a protein.
- OperonAn operon is a cluster of genes in bacteria that share one promoter, are switched on and off together and are copied into a single messenger RNA.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Transcription
- OpenStax Biology 2e, 15.2 Prokaryotic Transcription
- OpenStax Biology 2e, 15.3 Eukaryotic Transcription
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