Observe the given picture and answer the following questions.
Given below are two statements:
Statement I: In prokaryotes, control of the rate of translational initiation is the predominant site for control of gene expression.
Statement II: In eukaryotes, gene expression can also be regulated at the processing level, by regulation of splicing.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Statement I is incorrect but Statement II is correct.
Gene expression can be controlled at different levels. In bacteria the main control point is the start of transcription, while in eukaryotes control can also act on the RNA after it is made.
Statement I: In prokaryotes, control of the rate of translational initiation is the predominant site for control of gene expression. — False. NCERT says the predominant site in prokaryotes is the rate of transcriptional initiation. The activity of RNA polymerase at the promoter is regulated by activators and repressors, as in the lac operon shown in the figure. The word translational makes the statement wrong.
Statement II: In eukaryotes, gene expression can also be regulated at the processing level, by regulation of splicing. — True. In eukaryotes regulation can be exerted at four levels: transcription, processing (splicing), transport of mRNA from the nucleus to the cytoplasm, and translation.
So Statement I is incorrect and Statement II is correct.
NCERT Extract:
Regulation of Gene Expression – “Regulation of gene expression refers to a very broad term that may occur at various levels. Considering that gene expression results in the formation of a polypeptide, it can be regulated at several levels. In eukaryotes, the regulation could be exerted at (i) transcriptional level (formation of primary transcript), (ii) processing level (regulation of splicing), (iii) transport of mRNA from nucleus to the cytoplasm, (iv) translational level.”
Regulation of Gene Expression – “… In prokaryotes, control of the rate of transcriptional initiation is the predominant site for control of gene expression. In a transcription unit, the activity of RNA polymerase at a given promoter is in turn regulated by interaction with accessory proteins, which affect its ability to recognise start sites.”