How would RNA polymerase be affected if the repressor protein were not bound to the proper site on a gene?

1 Answer
Nov 15, 2016

The name REPRESSOR tells its own story: when a repressor protein attaches itself on DNA, it inhibits transcription of the DNA. In absence of repressor protein RNA polymerase will attach to DNA and corresponding RNA molecule will be formed.

Explanation:

Gene is a stretch of DNA. It contains recipe of a protein in coded language. The recipe must be copied on a short RNA molecule by a process called transcription.

Transcription can take place in presence of RNA polymerase enzyme, which would open the DNA double helix along gene to create a complementary RNA from template DNA strand.

www.mun.ca

The RNA polymerase can not attach at any random site on DNA; for this special promoter site is present just before the gene. Between promoter and gene another site is present called operator site.

www.dnacoil.com

Repressor protein can attach at operator site and this binding prevents RNA polymerase molecule to travel along DNA towards genetic sequence. Hence transcription of gene can not take place when repressor molecule is attached to operator site of DNA.

Generally in presence of an 'inducer' molecule, the repressor could be dislodged and RNA polymerase will slide down the genetic DNA to complete transcription.

From the following illustration you would understand role of repressor protein in prokaryotic lac operon

image.slidesharecdn.com
images.slideplayer.com