Imagine a gene with $n$ exons and $m$ introns. How many proteins are possible from that gene? Would all the proteins be isoforms?

  • $\begingroup$ Is this a homework question or a assignment? If so, please tag it accordingly and tell us what you have done to solve this. $\endgroup$ – Chris May 2 '15 at 8:01
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    $\begingroup$ This question cannot be answered in its current form. How many of the exons contain a valid START codon? How many exons are in UTRs? How many actually code for protein and don't contain in-frame STOP codons? Please edit and make it more specific. $\endgroup$ – terdon May 2 '15 at 9:09

I might be wrong, but aren't numbers $n$ and $m$ are connected as $n=m+1$?

Answer seems to be combinatorial: how many combinations of $n$ objects can be assembled under certain restrictions? Namely, how many isoforms certain gene can have.

Restrictions include: how many exon-intron junctions on codon (or precisely between codons), how many exons are actually contain protein-coding sequence of mRNA (some exons are coding untranslated region, 3'- or 5'-UTR, for example), how certain gene processes alternative splicing.

So, as you can see, answer will highly depend on sequence of given gene. As far as I know, maximum number of isoforms is limited by 5, even though there are genes with hundreds of exons.

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