What is the purpose of introns in DNA?

Question

Introns are just spaces inbetween exons in DNA. They do not contain any information, and just seem to be there. What is the purpose? Also, is it true that eukaryotes have introns, prokaryotes do not?

Answer 1

Intronic sequcences are evolutionary hold-overs. Basically, they are genetic material that was copied over while the organism evolved, but their purpose is under debate. Prokaroytes do have introns, but they are much more infrequent. Thus, the theory that introns evolved over time has some merit, for the more complex organisms have the most intronic sequences. Introns, as many scientists believe, are hypervariable regions within genes. Since they don't undergo the normal selection pressure that exons do, they can change quite a bit from generation to generation (though, more likely over many generations). When a chance mutation changes the exon-intron boundry, introns can increase or decrease in size, altering protein function. This is postulated to provide the wide array of proteins and regluatory systems in the cell that we observe in living cells. Additionally, introns may produce their own RNA, in a sense, that provides transcripts for proteins that are in the process of evolution, also allowing regulation of other established genes.

This is a good opinion paper to read on the subject:
http://www.imb.uq.edu.au/download/large/Introns_1994.pdf

Answer 2

Introns separate exons and they control when the exons can be used in protein synthesis, so they control when certain proteins are made. They can control when certain genes are used, such as some that are only "turned on" during infancy or or adolescence. Thus, introns do actually serve a purpose, although it does seem at first that they are just taking up space on the chromosome.

I am pretty sure that no, prokaryotes do not have introns.

Answer 3

Introns often are just gaps between exonic DNA (i.e. DNA that codes for proteins).

However, they may also regulate a phenomenon called alternative splicing where a gene may select different sections of DNA to make slightly different proteins with slightly different functions. This is actually now known to be extremely common in the genome.

In addition, some introns produce RNA which may have their own catalytic activity (they are called ribozymes).

Prokaryotes actually consist of two groups - archaea (related to eukaryotes) and bacteria. There are species in both groups which have introns in their DNA, often acting as ribozymes.

Answer 4

The exact nature of introns is not yet known, although recent research as suggested that they may have a role in gene regulation via an RNAi like "micro RNA" mechanism, in which the intron contains sequences complementary to a specific gene sequence. when the micro RNA binds to this sequence, the entire RNA complex will then be destroyed...
this is a very new mechanism that has just recently been discovered, and more research is currently being done to resolve the entire and exact mechanism by which this occurs.

As far as prokaryotes having introns or not, i'm not sure about that....

Answer 5

I can't answer the second part of your question, but I know prokaryotic DNA is just a circular strand inside the cell. I have heard that introns may contain vestigial DNA or the DNA left over from our ancestors. You might be suprised at how much of the human genome does not actually contribute to anything (we are mostly junk DNA). We don't lose the genes of our ancestors, they are just no longer expressed. An example would be the activity of the appendix (today has no function, but 200,000 it was thought to be used in digestion of raw meats?) I might be wrong on this....