Talk:Exon

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Article Grading: The following comments were left by the quality and importance raters: (edit · history · refresh · how to use this template) Rated "high" as high school/SAT biology content, part of gene structure. - tameeria 23:48, 18 February 2007 (UTC)

I think that the ORF is the sequence that is between a start and a stop codon...

[edit] Exons that do not correspond to protein are not exons

The current Wikipedia entrance on Exons claims that exons are INCORRECTLY referred to stretches of DNA that do correspond to coding DNA. The reasoning behind this is a reference to a paper that discusses this types of exons. One paper does not merit to change a definition of something that is found in all textbooks and all glossary as: Coding sequence of DNA present in mature messenger RNA. EXpressing regiON. This whole entrance is INCORRECT and should be changed.

Regarding the remark above this one: if you refer to a mRNA you are correct, if you refer to hnRNA or the gene you are wrong since these might contain INTeRvening regiONs

Glossary definition of exon, from the Lodish textbook: Segment of a eukaryotic gene (or of its primary transcript) that reaches the cytoplasm as part of a mature mRNA, rRNA, or tRNA molecule.

As far as I know, everybody in genomics recognizes that exons need not contain protein-coding sequence; 3' and 5' UTR exons are found in most eukaryotes, and there are even entirely non-protein-coding transcripts that undergo splicing. Exons that do contain protein-coding sequence are referred to as CDS exons when the distinction is important. --Mike Lin 21:20, 11 July 2006 (UTC)

The Wikipedia entry is correct not all exons code for proteins. Although a search of online definitions [1] finds many entries that imply exons must code for proteins. Most will, although a significant amount of exons code for UTRs see the entry on 3'UTRs.

TransControl (talk) —Preceding comment was added at 03:21, 22 February 2008 (UTC)

[edit] Conflicts with Complementary DNA

Got this from the Complementary DNA entry:

The central dogma of molecular biology outlines that in synthesizing proteins, DNA is transcribed into mRNA, which is translated into protein. One difference between eukaryotic and prokaryotic mRNA is that eukaryotic mRNA can contain introns (intervening sequences), which are not coding sequences, per se, and must be spliced out of the mRNA before it is translated into protein. Prokaryotic mRNA has no introns, so it is not subject to splicing.

And this from the Exon Entry:

An exon is any region of DNA within a gene that is transcribed to the final messenger RNA (mRNA) molecule, rather than being spliced out from the transcribed RNA molecule. Exons of many eukaryotic genes interleave with segments of non-coding DNA (introns). The term exon was coined by American biochemist Walter Gilbert in 1978:

So we have "eukaryotic mRNA can contain introns" and "An exon is any region of DNA within a gene that is transcribed to the final messenger RNA (mRNA)". Those can't both be true.

I'm guessing that the statement under Exon is supposed to be "eukaryotic RNA can contain introns". Not mRNA. But I don't know from biology. :) —The preceding unsigned comment was added by 155.104.37.17 (talk) 20:13, 6 March 2007 (UTC).

[edit] Confusing

The current opening is confusing:

"An exon is any region of DNA within a gene that is transcribed to the final messenger RNA (mRNA) molecule, rather than being spliced out from the transcribed RNA molecule. Exons of many eukaryotic genes interleave with segments of non-coding DNA (introns)"

but not incorrect

I suggest this rewrite-

An exon is the region of a transcribed gene present in the final functional RNA molecule, whereas intragenic introns are spliced out.

Note: a) part of every mature mRNA is non-coding UTR but exonic. As in the diagram and text. b) other RNAs, tRNAs etc have introns c) However, introns, by definition do not code for proteins. (At least in the mRNAs they are removed from.) d) There is some lack of clarity as to whether the exon is part of the gene (DNA) or mRNA, or both.

Many web definitions are not correct:
http://www.biochem.northwestern.edu/holmgren/Glossary/Definitions/Def-E/exon.html
http://www.answers.com/topic/exon?cat=technology
as they imply that exons always code for proteins, whereas they do not, as correctly pointed out in the article.

This prominent Molecular Biology online text book has a definition similar to that proposed, but it is more complex:

http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.glossary.4754

TransControl (talk) —Preceding comment was added at 04:23, 20 February 2008 (UTC)