The genetic information that is passed on from patent to offspring is carried by the DNA of a cell. The genes on the DNA code for specific proteins determine appearance, different facets of personality, health, etc. In order for the genes to produce the proteins, it must first be transcribed from DNA to RNA in a process known as transcription. Thus, transcription is defined as the transfer of genetic information from the DNA to the RNA. The process of transcription occurs in the nucleus of the cell. There are three different phases involved : initiation, elongation and termination. To initiate the process of information transfer, one of the strands of the double stranded DNA serves as a template for the synthesis of a single strand of RNA that is complementary to the DNA strand. The enzyme RNA polymerase binds to a particular region of the DNA that is termed as the ‘promoter’.
The promoter is a particular unidirectional sequence that appears at the beginning of the genes, and tells the enzyme where to start the synthesis and which strand to synthesise. Once the enzyme is bound to the promoter, it unwinds the DNA and starts to make a strand of RNA with a base sequence complimentary to the DNA template that is downstream of the RNA polymerase binding site.
The strand from which it copies is known as the template of the antigenes strand, while the other strand to which it is identical is called the sense or the coding strand. After initiation, is the process of elongation. The substrates for RNA polymerase are nucleoside triphosphates. The RNA polymerase match a base on the DNA to a RNA nucleoside (by complimentary base pair binding) and then adds that nucleoside to the elongating RNA strand. The next phase is called termination. Termination occurs when the RNA polymerase reaches a signal on the DNA template strand that tells it to stop. Once this termination signal is recognised by the RNA polymerase, it releases the DNA and transcription ceases. The newly synthesised RNA strand now undergoes ‘post-transcriptional processing1.