Transcription (genetics)
Transcription (genetics) is the first step of gene expression, in which a particular segment of DNA is copied into RNA by the enzyme RNA polymerase. Both DNA and RNA are nucleic acids, which use base pairs of nucleotides as a complementary language. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallel RNA strand called a primary transcript.
Process[edit | edit source]
Transcription can be explained in 5 major steps: pre-initiation, initiation, promoter clearance, elongation, and termination.
Pre-Initiation[edit | edit source]
In the pre-initiation step, the RNA polymerase is attached to the DNA at the promoter region, then it forms a transcription bubble which is the region of DNA that is being transcribed.
Initiation[edit | edit source]
During initiation, the RNA polymerase starts to synthesize the RNA transcript. This process requires a series of transcription factors.
Promoter Clearance[edit | edit source]
After the first bond is synthesized, the RNA polymerase must clear the promoter. During this time there is a tendency to release the RNA transcript and produce truncated transcripts. This is called abortive initiation and is common for both eukaryotes and prokaryotes.
Elongation[edit | edit source]
Once promoter clearance is complete, the RNA polymerase is released from the promoter. The polymerase then proceeds to the elongation phase, during which the RNA transcript is extended.
Termination[edit | edit source]
Once a gene is transcribed, the prokaryotic polymerase needs to be instructed to disassociate from the DNA template and liberate the newly made RNA. There are two kinds of termination signal: rho-dependent termination and rho-independent termination.
See also[edit | edit source]
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