Transcription
How the information in a DNA gene is copied into RNA — the first step in gene expression and the point at which much regulation is exerted.
Definition
Transcription is the enzymatic synthesis of an RNA molecule using one strand of DNA as a template, carried out by RNA polymerase and producing messenger, ribosomal, transfer, and other RNAs that follow from the information encoded in the gene.
Scope
This area covers DNA-dependent RNA synthesis from initiation through termination, including the RNA polymerases, the promoter and factor recognition that selects where transcription starts, the elongation step, the maturation of primary transcripts into functional RNAs, and the signals that stop synthesis. It treats transcription as a mechanism and a control point; downstream translation and the broader logic of regulatory networks are covered in neighbouring areas.
Sub-topics
Core questions
- How does RNA polymerase find a gene and begin synthesis at the right place?
- Which strand is used as a template and how is the RNA built?
- How is a primary transcript processed into a mature, functional RNA?
- How does the cell know where to stop transcribing?
Key theories
- Central dogma — DNA to RNA
- Sequence information flows from DNA into RNA by transcription, defining RNA as the intermediary that carries the genetic message toward protein synthesis, as articulated in Crick's statement of the central dogma.
- Template-directed, single-strand synthesis
- RNA polymerase reads one DNA strand and synthesises a complementary RNA 5'→3' without a primer, transcribing defined units rather than copying the whole chromosome.
Mechanisms
Transcription proceeds in three phases. In initiation, RNA polymerase, guided by promoter sequences and (in eukaryotes) general transcription factors, binds and melts the DNA to form an open complex and begins RNA synthesis. In elongation, the polymerase moves along the template, extending the RNA and maintaining a transcription bubble. In termination, specific signals release the polymerase and the completed transcript. In eukaryotes the primary transcript is further processed — capping, splicing, and polyadenylation — to yield the mature RNA.
Clinical relevance
Because transcription is the principal control point of gene expression, its components and regulators are widespread drug targets and are dysregulated in many diseases; this is offered as significance rather than as clinical guidance.
History
The discovery of messenger RNA and of RNA polymerase in the early 1960s established transcription as a distinct step; Crick's 1970 restatement of the central dogma fixed its place in the flow of genetic information, and later structural work on RNA polymerase detailed the mechanism now taught as standard.
Key figures
- Francis Crick
- Roger Kornberg
- Robert Roeder
Related topics
Seminal works
- crick1970
- watson2013
Frequently asked questions
- What is the difference between transcription and replication?
- Replication copies the whole genome into DNA for cell division, while transcription copies individual genes into RNA as the first step of expressing them.
- Is the whole DNA molecule transcribed at once?
- No. Transcription acts on defined transcription units, starting at promoters and ending at termination signals, so only selected regions are copied into RNA at any time.