Question

Describe the initiation process of transcription in Bacteria ?



class 12th CBSE Biology sample paper

Answer 1

There is a convention in defining the two strands of the DNA in the structural gene of a transcription unit.  Since the two strands have opposite polarity and the DNA-dependent RNA polymerase also catalyse the polymerisation in only one direction, that is, 5'→3', the strand that has the polarity 3'→5' acts as a template, and is also referred to as template strand. The other strand which has the polarity (5'→3') and the sequence same as RNA (except thymine at the place of uracil), is displaced during transcription.  Strangely, this strand (which does not code for anything) is referred to as coding strand.  All the reference point while defining a transcription unit is made with coding strand.

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In bacteria, there are three major types of RNAs: mRNA (messenger RNA), tRNA (transfer RNA), and rRNA (ribosomal RNA).  All three RNAs are needed to synthesise a protein in a cell.  The mRNA provides the template, tRNA brings aminoacids and reads the genetic code, and rRNAs play structural and catalytic role during translation. There is single DNA-dependent RNA polymerase that catalyses transcription of all types of RNA in bacteria. RNA polymerase binds to promoter and initiates transcription (Initiation). It uses nucleoside triphosphates as substrate..

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 The RNA polymerase is only capable of catalysing the process of elongation.

The initiation is associates transiently with initiation-factor (σ)