Gene A-------------Gene B-------------Enhancer-------------Gene C-----------Insu
ID: 218315 • Letter: G
Question
Gene A-------------Gene B-------------Enhancer-------------Gene C-----------Insulator-------------Gene D
our genes (A, B, C, and D), an enhancer and an insulator are organized as shown in the diagram. They are considered close together; the region shown is a total of 10kb in length. Gene C uses the bottom DNA strand as the template strand for transcription whereas Genes B and A use the top strand as the template strand for transcription. Which gene(s) will be transcribed at the basal level? Which will be transcribed at the induced level?
Write a few sentences to answer the questions and Explain your reasoning.
Explanation / Answer
Answer:
Gene-D will be transcribed at the basal level. The reason behind this is that, it has an insulator molecule prior to its gene sequence. So, an insulator molecule will bind itself in the middle of the sequnces of enhancer molecule and a promotor. As a result, there is not room for the proper attachment of the RNA polymerase, so no transcription could be continued till an insulator molecule is removed. Another reason being, sometimes, due to complementry base pairing between 2 gene sequences, there is a formation of the hair pin loop like structure. If due to presence of insulator, small loop is formed which exposes the termination sequences and thus, there will be a formation of premature transcript.
Gene-C will be transcribed at the induced level. This is because, prior to the Gene-C there is a presence of enhancer molecule which will help in exposing the promotor sequence which will further allow the proper binding of the RNA polymerase along with other factors required for the transcription process.
[Note that, whenever an enhancer/insulator molecule is present, they will always effect the gene expression of the next gene present and no effect will be there on the genes present upstream of such molecules]
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