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Data is available on just over a million of them, taken mainly from information found in the over genomes that have been fully sequenced.
The field that analyzes proteins in general and aims to exhaustively characterize all of those in the human body is called proteomics. Many see the next logical step after the completion of the Human Genome Project to be the initiation of a Human Proteome Project. The Human Proteome Organization was founded to pursue this goal.
Proteins are long molecular chains made from the 20 basic building blocks of life, amino acids. The longest known one, titin, also known as connectin, contains 26, amino acids. Titin is found in muscle and contributes to its passive stiffness. How many alternatively-spliced proteins are actually known and the alternatives known to be functional? I only know of one, MYC, which has two forms, but I only know about it because I happen to have sequenced it.
Is there a review of functional alternative splicing in some taxon or taxa? John, perhaps the first comment to this post has a tiny bit of what you are looking for. Are you a big fan of Arabidopsis?
Better yet, is there a review of alternative splicing in Arabidopsis so I don't have to wade through those various references?
Finally, any estimate of the average number of functional transcripts per gene? I don't know about plants but in mice it's supposed to be one major transcript per gene. Transcriptome analysis of human tissues and cell lines reveals one dominant transcript per gene. Genome Biol. Sorry, the aboven mentioned paper is on human tissues as the title actually states. Working with mice let me forget men sometimes.
Even that paper has a significant "miss" in the results section when they get hung up on the fact that "Genes with major non-coding transcripts are expressed at higher levels in the nucleus, compared to those with major coding transcripts, while this trend is inverted in the cytosol" Saying an one form of an mRNA is "expressed" in the nucleus and a different form is "expressed" in the cytosol is biochemical nonsense. They do address this somewhat better in the discussion, but it shouldn't have needed discussion!
There are something like different post-translational modifications known to be found among the core histones alone, i. Obviously the true complexity is not that high since many marks will be mutually exclusive, and other marks will be strongly correlated with each other. Ironically, this is the same mistake made in the opposite sense by people like John Mattick - they assume that a huge number of genes is necessary to specify the uncountable number of of different heritable phenotypes, missing the point that with just a handful of different transcription factors working together you could trivially end up with a unique combination for every individual cell in the body of every individual animal on the planet.
Now, in regard to the histone code, the question of how much of the variation is functionally relevant is a very different story. Sticking an acetyl group onto one lysine or the next door lysine is, strictly speaking, a different modification. However, the net effect of adding a charged residue to a particular region of the histone surface may well be much the same. At the moment I'd say we're not doing that well at working out which differences are meaningful and which are not, and that's because cells sometimes care about single atom differences, and sometimes they don't!
I'm focusing on the histone code there because Larry says that PTMs are "genuine versions of different proteins although you probably wouldn't want to make a fuss about it", and also because unlike Larry's example of N-terminal signal peptides, there is no final terminal "steady state" for histones.
Every modification potentially has a different meaning, but we don't yet know what they are. Realistically, I guess you could set an upper bound on the meaningful diversity of the histone code by working out how many "readers" there are and what their specificities are no I don't know the number and nor does anyone else.
Then add on a few for the modifications that don't have direct readers but are meaningful in regulating nucleosome removal, replacement etc. In the case of histones these modifications may have been selected for. I don't know how likely this scenario is but wouldn't that be noise which is not selected against and thus retained by the cell?
Oh certainly. I'm sure there are whole fields of new noise waiting to be discovered. Just because kinase A phosphorylates target B, that doesn't mean there's any functional relevance to it. Story Source: Materials provided by University of Toronto. Cell Systems , ; DOI: ScienceDaily, 17 January University of Toronto. A cell holds 42 million protein molecules, scientists reveal. Retrieved October 25, from www. Researchers have now elucidated the transport path On one hand, the protein is described as a cell proliferation The protein enables the fusion of two cells, such as a sperm cell and egg cell, or ScienceDaily shares links with sites in the TrendMD network and earns revenue from third-party advertisers, where indicated.
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