Start Point – It is the first base pair from where transcription starts and is called start site. RNA polymerase moves from start point along with template, synthesize RNA up to terminator sequence.
Upstream –It is nontemplate nucleotide in 5’ end or minus direction; sequence before start point.
Downstream-It is nucleotide in 3’ end or plus direction; sequence after start point. DNA is a double stranded structure. During transcription only one strand is transcribed so that transcribed sequence is identical with one strand of DNA, known as Coding or sense strand and other complementary strand is known as template or antisense strand (Figure 28.2).
Figure 28.2 : Difference between coding and non coding strand
TRANSCRIPTION: The molecular process through which cell form RNA from DNA is called as transcription. The basic steps of transcription remain same between prokaryotic and eukaryotic organism and few of the selected differences are outlined in the Table 28.1.
TRANSCRIPTION IN PROKARYOTES
A) RNA Polymerase: In prokaryotes single type of RNA polymerase is present which is responsible for synthesis of all type of RNA. Eubacterial RNA pol is named as Holoenzyme is a multisubunit protein which contain five subunits ααββϭ , structure of RNA polymerase is given in Figure 28.3.
Figure 28.3 : Structure of RNA Polymerase |
α- assembly of core enzyme |
