Introns and more

[evointrigued]

- Why are introns important to evolution? If they're not expressed, what's the use?
- Does the fact that several mRNA molecules can be transcribed from one gene, mean the potential rate of gene expression in increased?

[BioCore]

I am not entirely sure myself but from an evolutionary point of view, this would be an effective way of storing more information in DNA. Introns help divide the exons of the mRNA message, and these exons can be spliced in different ways in order to create different mRNA messages - ultimately different proteins. This means that one gene can hold the code for multiple proteins, maybe even more than the (I think it was 20,000-25,000 genes last time I checked in humans).

Now I am not sure I understood your last comment, but what this ultimately leads to is a better method of storing, and does not cause the rate of translation to increase.

[jonmoulton]

Besides being evolutionary scratchpads, where DNA sequence changes can accumulate and later find their way into expressed sequences by events such as mutations that create splice sites, introns can also host some functional sequence such as micro-RNAs (miRNAs). While these sequences are not expressed as protein, they are important in modulating expression of other genes. Not all miRNAs are in introns, but those that are present interesting examples of functional sequences located in introns.

[Darby]

The presence of introns also minimizes the effects of frame-shifting point mutations. An insertion, for instance, only shifts the codons a spot until the next intron.

It's possible that such a system is more likely to produce a significant change in a coded protein without making it totally useless.

[wbla3335]

An insertion, for instance, only shifts the codons a spot until the next intron.

Are you sure about that, Darby?

[MrMistery]

Darby is correct. Why do you think he is mistaken?

[wbla3335]

Early-onset dementia? How does the presence of an intron downstream from a frameshift in genomic DNA undo the frameshift in the mRNA?

[MrMistery]

no, sorry, you're right... I was doing to much math yesterday I guess

[Darby]

I'm not sure of the mechanism, I just know I've run across the statement more than once.

[beautifulmind420]

Introns are important because they may contain regulatory regions of coding sequences.

[MrMistery]

that is true sometimes. However, it is pretty rare. The main advantage introns bring is the possibility of generating protein isoforms. Humans can produce somewhere between 80 and 100,000 proteins from 21,000 genes.

[keenangp]

Darby is correct methinks.. But the process only works if the code causing the frameshift is found in an intron.

ex.

transcript with intron:
|AAUUGG|AAUCGG|AAUUGG|
mRNA:
|AAUUGG|AAUUGG| - functional

transcript without intron:
|AAUUGGAAUCGGAAUUGG|
mRNA:
|AAUUGGAAU*********| -not functional

greater probability of excising a mutation right..?