Transcription is the copying of DNA into complementary mRNA.
Transcription is an important step in protein synthesis and occurs inside the nucleus. It can be broken down into three steps:
Initiation: Enzymes such as RNA polymerase (RNAP) bind to the promoter region of the gene.
A small section of the DNA is unwound, exposing the bases for transcription. Only one strand of the DNA is transcribed and used as a template for protein synthesis.
Elongation: Complementary RNA nucleotides assemble alongside the DNA template. RNA polymerase catalyses the formation of phosphodiester bonds between the RNA nucleotides.
Termination: Transcription ends when RNA polymerase reaches the terminator sequence, a section of non-coding DNA positioned just downstream of the gene.
The terminator sequence causes the polymerase to unbind from the DNA. A single strand of mRNA is released.
The promoter region is the section of DNA that indicates where a gene begins. This region initiates transcription.
Enzymes that initiate transcription of mRNA bind to promoter regions.
In prokaryotes, there is a promoter structure known as the TATAAT box. Its name reflects the base sequence.
The TATAAT box is positioned about 10 bases in front of the first base of the gene (upstream of the gene) and is essential for transcription.
About 35 bases upstream of the gene, there is another promoter region with the sequence TTGACA. This sequence alters the rate of transcription (the number of mRNA molecules transcribed in a given time)
Eukaryotic promoters are more diverse and less regular than prokaryotic promoters. There are some common promoters, like the TATA box (sequence TATAAA).