The complexity of DNA goes far beyond what we call ‘genes’ – 02/29/2024 – Darwin and God

I had to write a reportabout the possible genomic mechanisms behind tail loss in our ancestors to make a point (I know, an old-fashioned expression) that should have dropped a long time ago: the image that almost everyone has about the way DNA works is an absurdly old-fashioned thing, especially when we talk about “genes “.

The definition of “gene” that people learn in high school (at least those who have not been or are not yet subjected to the educational excrescence dubbed “new high school”) is a relatively simple matter. According to this view, DNA contains, in its chemical “letters”, the recipe for the production of proteins. Each gene in DNA would correspond to a sequence of almost equivalent letters of RNA (DNA’s “primary” molecule). And the RNA corresponding to that gene, in turn, would serve as the basis for the production of a single protein in the organism.

It turns out that, to begin with, the correspondence “1 gene = 1 RNA molecule = 1 protein” simply does not exist in most living beings. And the results of research into the absence of tails in primates like us depend precisely on this to make sense.

In fact, genes are commonly composed of (at least) two very different parts: introns and exons. Exons seem, at first glance, to correspond to the antigenic definition of a gene: they are what effectively serve as the basis for the manufacture of proteins. Introns are regions of DNA that even become RNA, but are edited — cut out by specific mechanisms — before the production of protein components.

It seems like a lot of work for nothing, from our point of view, right? Why produce the entire RNA if the introns are going to be cut anyway?

Well, it turns out that there is something called “alternative splicing”: under certain conditions, you can combine exons in different ways, leaving one or the other out. Result: more than one protein coming from “the same gene”. (To make matters worse, some exons also don’t end up becoming proteins anyway, but can have other functions.)

But wait, it gets worse. Even outside of introns, there are numerous regions of DNA that appear to be “not useful” and yet, under different circumstances, can decisively influence how a protein is produced. In the study of the end of the tails of great apes and humans, this role falls to the “Alu elements” that I mentioned in the linked report. They are spread throughout the human genome and, at least in this case, they have a crucial function.

Two of them, arranged on opposite sides in different introns, make the cell “skip” reading an exon, thus turning off an apparently crucial mechanism for the formation of tails.

And this is just one example. There are many other modalities of influence that have nothing to do with genes and, sometimes, not even with RNA. It is no surprise that there is still a long way to go before we understand how genetic material influences the development and health of living beings.

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