What Are Introns? Understanding Their Role in Gene Expression

[Eagle9]

Good day!

I have read this interesting blog:
https://thehumanevolutionblog.com/2...ourney-through-the-dark-matter-of-the-genome/
There is explained what are introns (of course I knew the meaning of this term but I intentionally copied the following explanation from this blog):

Introns – the regions within a gene that do not encode for part of the protein and are instead “spliced out” of the mRNA before it is translated to protein.

Image from Wikipedia:

So, introns are part of mRNA, or gene(s) itself located in DNA, this is clear. The genes make up only 2-3 % of the whole DNA, so introns (or their predecessors) are located in this 2-3 %, right?
But this blog has got such image:

What do they mean? 26 % of whole genome belongs to the introns that (if I understood correctly) are part of 2-3 % of the same whole genome? Or maybe I misunderstood something?

 

[Ygggdrasil]

The 2% protein-coding genes refers only to the exons in genes (as only exons code for protein).

 

[Eagle9]

The 2% protein-coding genes refers only to the exons in genes

So, the introns hold 13 times (26/2=13) more space (I mean nucleotide numbers in DNA) than exons?

 

[Ygggdrasil]

So, the introns hold 13 times (26/2=13) more space (I mean nucleotide numbers in DNA) than exons?

Yup, that is correct. For example, here's a diagram showing the exons (thick bars) and introns (thin bars) for the various splicing variants of a fairly typical gene, GAPDH (encoding the glycolytic enzyme, glyceradehyde-3-phosphate dehydrogenase):

https://www.ncbi.nlm.nih.gov/gene/2597

As you can see, there is much more intronic, non-coding sequence in the gene than exonic, protein-coding sequence. Furthermore, of the exons, only the parts colored in dark green actually code for protein. The exonic regions in light green at the beginning and end of the transcripts encode the 5' and 3' untranslated regions of the mRNA, which do not get translated into protein.

Weird, right?

 

[Eagle9]

Yup, that is correct. For example, here's a diagram showing the exons (thick bars) and introns (thin bars) for the various splicing variants of a fairly typical gene, GAPDH (encoding the glycolytic enzyme, glyceradehyde-3-phosphate dehydrogenase):

https://www.ncbi.nlm.nih.gov/gene/2597

As you can see, there is much more intronic, non-coding sequence in the gene than exonic, protein-coding sequence. Furthermore, of the exons, only the parts colored in dark green actually code for protein. The exonic regions in light green at the beginning and end of the transcripts encode the 5' and 3' untranslated regions of the mRNA, which do not get translated into protein.

Thanks a lot

Weird, right?

Yes, weird and complex