8. During your summer research, you identified a gene that is expressed in the i

Question

8. During your summer research, you identified a gene that is expressed in the intestinal cells of mice and mutations in this gene are associated with Crohn's disease. Further analysis reveals... 1) That the coding sequence of the gene is the same in affected and wild-type (normal) mice. 2) While transcription of the gene is normal, there is much less mature mRNA produced in the affected mice relative to that in the wild-type mice. 3) The intestinal cells of the affected mice show no detectable protein unlike the wild-type mice. By considering the steps in eukaryotic gene expression, indicate the absence of which stepls) may explain the differences that you have observed between the affected and wild-type mice. [4 pts]

Explanation / Answer

Crohn’s disease is a chronic inflammatory bowel disease characterized by inflammation of the digestive or gastrointestinal tract. As transcription is normal in both the wild-type and affected mice but mature RNA produced in affected mice is lesser than normal mice making a lesser amount of proteins in the affected mice.

This clearly suggests that there occurred some differences in post-transcriptional modification of m RNA which involves splicing in which introns are removed from the mature m RNA transcript and exons are joined together. Introns are the non-coding sequences which are to be removed. Probably, in this case, removal of few exons have also taken place and this is the reason why coding sequence has been reduced, giving rise to lesser amounts of amino acids and a very small sized protein leading to Crohn`s disease.

This may have also occurred due to the lack of transcription of a few regions of DNA but as the question, says that transcription has been normal. This clearly suggests that there had been a problem that occurred after transcription. After transcription, there is only one phase and that is the post-transcriptional modification which involves many events and one of which is splicing which may have disturbed the protein status of affected mice.

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