Transcription

Transcription is the process by which single mRNA is coded from double stranded DNA. This process is highly regulated and controlled to ensure the right amount of a specific gene is coded for at a specific time.

Proteins are synthesised in the cytosol, however, DNA does not leave the nucleus, therefore a copy of the gene coding for the desired protein is sent as a messenger to the cytosol from the nucleus. This is called messenger RNA 'mRNA', which is a single stranded molecule that is a complementary copy of the DNA strand it was synthesised from.

DNA is double stranded as apposed to mRNA which is single stranded, therefore only one strand of DNA is copied. The copied strand is called the 'template strand', the other strand is called the 'non-template strand'. mRNA is synthesised by the enzyme 'RNA polymerase', however, in order for the RNA to synthesise mRNA it must bind to a single strand of DNA. The DNA must be unwound and unzipped, which is done via an enzyme called 'DNA helicase', which unwinds and unzipps the double stranded DNA at the loci of the gene to be transcribed, causing an area of single stranded DNA to be accessible to the RNA polymerase.

RNA polymerase must recognise and bind to a region upstream of the gene being transcribed called the 'promotor region'. This region is a sequnce of bases that determines the strength of the binding of RNA polymerase to the DNA strand and therefore determining the efficiency of trancription of the gene it is accossiated with. If the promotor is a strong promotor, then RNA polymerase binds strongly to the DNA strand. If the promotor is a weak promotor, then the RNA polymerase can become hindered and can even unbind from the DNA strand.