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Anonymous Annonn
wrote...
A month ago
You are studying a large eukaryotic gene that is 439,515 base pairs long. You find the polypeptide that this gene produces in liver cells is 46,771 amino acids long...


A) Based on the size of the gene, is the polypeptide as big as you would expect? How many amino acids would you expect to find? Explain the reason for any differences.


B) Your colleague studies the function of this gene in brain cells, and finds the polypeptide produced in the brain is much larger – 61,438 amino acids long. How do you explain this difference?

The cell cycle of liver cells is much longer than that of brain cells.
This is due to alternative splicing in the brain
There is no 5' cap added to the gene product from the liver cells.
There was a different complement of sequence-specific transcription factor binding sites in the CRM of the brain cells.
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Anonymous
wrote...
A month ago
Quote
A) Based on the size of the gene, is the polypeptide as big as you would expect? How many amino acids would you expect to find? Explain the reason for any differences.

No, it is smaller due to introns in the gene and other untranslated regions.

The size of a gene and the size of a polypeptide differs a lot because a lot of post transcriptional modification is performed on the gene which removes the unwanted regions and non-coding regions within the gene. These non-coding regions are called introns and UTRs (untranslated regions). With all this non-coding regions along with coding regions (exons), the size of gene is large. But after the removal of non-coding regions during splicing, the gene size reduces. So, after translation the size of polypeptide is quite smaller than the actual gene from where it was initiated. Thus, the real size of polypeptide is smaller than the expected size of polypeptide.

Quote
B) Your colleague studies the function of this gene in brain cells, and finds the polypeptide produced in the brain is much larger – 61,438 amino acids long. How do you explain this difference?

This is due to alternative splicing in the brain
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