Triple-helix DNA?

[Xyph]

Does it exist? Can it exist? Could it evolve naturally? Are there any inherent advantages to being a triple-helixed animal? How would a triple-helix lifeform differ from a double-helixer? What about multiple helixes? What effects would DNA of multiple helixes have on the creature that possessed it?

[the tree]

No, for exactly the same reason that you can't have a ladder with three legs.

[insane_alien]

err... i've seen a ladder with 3 legs. but i get what you mean.

[Xyph]

I'm sure a ladder with 3 legs could work, it'd just be more complicated, or 2 people could climb it at once if it was leaning on something. Anyway, a Google for "triple helix DNA" yields plenty of results, but I don't really know enough about biology to understand any of it - so what are they all about?

[Skylark]

Triple helix DNA occurs when a third oligonucleotide sequence occupies the major groove of double-stranded DNA.

[Xyph]

And what effects does it have?

[LucidDreamer]

"Triple helix DNA alters nucleosomal histone-DNA interactions and acts as a nucleosome barrier.

Oligonucleotides which form triple helical complexes on double-stranded DNA have been previously reported to selectively inhibit transcription both in vitro and in vivo by physically blocking RNA polymerase or transcription factor access to the DNA template. Here we show that a 16mer oligonucleotide, which forms triple helix DNA by binding to a 16 bp homopurine segment, alters the formation of histone-DNA contacts during in vitro nucleosome reconstitution. This effect was DNA sequence-specific and required the oligonucleotide to be present during in vitro nucleosome reconstitution. Binding of the triple helix oligonucleotide on a 199 bp mouse mammary tumour virus promoter DNA fragment with a centrally located triplex DNA resulted in interruption of histone-DNA contacts flanking the triplex DNA segment. When nucleosome reconstitution is carried out on a longer, 279 bp DNA fragment with an asymmetrically located triplex site, nucleosome formation occurred at the border of the triple helical DNA. In this case the triplex DNA functioned as a nucleosome barrier. We conclude that triplex DNA cannot be accommodated within a nucleosome context and thus may be used to site-specifically manipulate nucleosome organization."

 

Nucleic Acids Res. 1995 June 25; 23(12): 2184–2191

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=307006

[Xyph]

Haha, I understood almost none of that. Any chance of a simplification?

 

Is it saying that creatures can't be built entirely from triple helix DNA?

[LucidDreamer]

Well, its saying that machinery involved in transcription (the process where DNA is copied to RNA) is prevented from working correctly when you use a triple helix instead of a double helix. So, that means that the current system of storing and translating our genetic code cannot operate with a triple helix. That could be just because life evolved around a double helix and doesn’t mean that a triple helix system isn't possible. Also, these studies were done on Eukaryotes, so you can't tell what effects a triple helix might have on a prokaryote from this article.

[Xyph]

Ah, thanks. So, if life had evolved around a triple helix, would it externally be much the same as double helix life? Or is there no way to tell what differences there might be?

[LucidDreamer]

No way to tell. My guess is that it would be quite different because of the whole "butterfly effect."

[Skylark]

If you think of the role of DNA as solely to transmit genetic data, then I doubt a life form based on triple helix DNA would be that different if the triple helix could transmit the same amount of genetic data. I think the only difference between the double and triple helix would be in the energetic costs of DNA replication and translation. Presumably the triple helix would have a higher cost which would mean an organism using this type of DNA would need a higher metabolic rate to compensate. I would suspect this wouldn't make a dramatic change in the gross external morphology of the organism as warm-blooded tetrapods aren't that dramatically different from cold-blooded tetrapods relatively speaking even though their metabolic rates are many times greater.

[Helix]

Yes triple helix can, and does, exist. It is akin to adding half a ladder to a whole one. In fact oglionucliotides, the name for triple helixes, are being used extensively in anti-cancer therapys. Because a triple helix cannot be copied, scientists are trying to turn the mRNA of mutant genes into a triple helix in order to silence it.

 

Also has some bearing to iRNA and siRNA, a biological mechinism that silences mRNA that is overexpressed.

[donkey]

oligonucleotides are not the name for triple helices btw, they are simply a short stretch of single stranded (single helix - err kinda) DNA. Also, i think you probably mean RNAi and not iRNA but yeah i'll stop nitpicking now

[Helix]

Yeah i noticed my gaff about 20 minutes ago while thinking about oglionucliotides. Which brings me to: yes that is correct to the point of "before conjunction." I think after the triple helix is created it keeps the name. At least, I was getting at the oglionucliotides function, which answers the inital question.

[starbug1]

Apart from anti-cancer therapy with oglionucleotides, is there no room for natural mutation. After all, a triple-DNA may be what makes up extraterrestrial lifeforms.

Now that we have legitimate prove of triple-DNA sequences, how about quad-DNA structure??!!??

[Helix]

Apart from anti-cancer therapy with oglionucleotides' date=' is there no room for natural mutation. After all, a triple-DNA may be what makes up extraterrestrial lifeforms.

Now that we have legitimate prove of triple-DNA sequences, how about quad-DNA structure??!!??[/quote']

 

 

Well no, that wouldn't work. If the extraterrestial life would use DNA it obviously operates the way we do. And oglionucliotides cannot be transcripted, let alone quad-nucliotides. That's the reason they're used in anti-cancer therapys, they block transcription of certain genes.

[ecoli]

Well no, that wouldn't work. If the extraterrestial life would use DNA it obviously operates the way we do. And oglionucliotides cannot be transcripted, let alone quad-nucliotides. That's the reason they're used in anti-cancer therapys, they block transcription of certain genes.

 

Only if you use enzymes compatible with double stranded DNA. Who is to say that extraterristrial life could form a ligase to replicate 3 or 4 or n strands of DNA?

[Ricker]

Sadly, I've never heard about the Triple Helix DNA, so I'm kinda new. My question is do they have the same bases such as Adenine, Cytosine, Guanine, and Thymine? I'm guessing that it would have an affect on the nucleic acid that is created when it comes all down to it. Just wondering, thats all.

[Helix]

Only if you use enzymes compatible with double stranded DNA. Who is to say that extraterristrial life could form a ligase to replicate 3 or 4 or n [/i']strands of DNA?

 

 

That's true, and pretty interesting. Now we think of life in two ways: "life as we know it (us)" and "alien (not us)". What if some alien species used triple, quadruple or even hexagonal (I'm not using the word correctly, I'm aware. The real word slipped my mind) DNA. This would blur the line for sure, and they would be far more complex (3,4,6-times the complexity of our genes.

 

But back on topic, and to answer the initial question, they do exist. Now I am wondering if they can help with diseases like cancer..?

[LucidDreamer]

Only if you use enzymes compatible with double stranded DNA. Who is to say that extraterristrial life could form a ligase to replicate 3 or 4 or n [/i']strands of DNA?

I wouldn't say that it would be impossible, but I believe that it might be improbable. I admittedly don't know a great deal about 4 stranded DNA, but from what I know about double stranded DNA I don't think that a 4 stranded DNA molecule would be very stable. Since we assume that chemistry on other planets will work similar to our own I think a 4 stranded molecule would not be useful and therefore it would be not selected during evolution.

[calbiterol]

Does it exist? Can it exist? Could it evolve naturally? Are there any inherent advantages to being a triple-helixed animal? How would a triple-helix lifeform differ from a double-helixer? What about multiple helixes? What effects would DNA of multiple helixes have on the creature that possessed it?

 

Hahahaha! Spose it's possible, and I'd tend to agree with the more biologically adept in this forum. What I think is funny is where I think you're getting the idea. Shall I be looking for a thread on weird spiral-shaped EM interference as well? What can I say, if you ask me, TV science is generally a contradition in terms.

[Xyph]

Not being a biologist, I obviously got the idea from science fiction, but I don't see what's so funny about trying to find out whether there's any truth to it. It's an interesting idea.

 

I presume "spiral-shaped EM interference" is a reference to another fictional idea, but I have no idea how it relates to this otherwise.

[calbiterol]

I apologize if I have offended. There's nothing funny about finding out if there's truth in it, indeed, I do the same all the time and encourage it. Many foundations of modern science are based on the science fiction of the past.

 

The thing that made me laugh was what I must now relate as an extremely unlikely coincidence. There is currently a rather scientifically unfounded (read: pure fiction, with pseudoscience mixed in, probably deemed science fiction) TV show on Friday nights here in the US that includes in its impressively implausible resume the ability of an alien species (possibly a 4- or 5-dimensional one at that) to modify the human genome to a triple helix. The timing was such that I believed this to be where you got the idea; apparently, this is not the case. Had I looked at your location, I could have easily discovered this. The reference to spiral EM interference patters was the alien species's calling card: burned into almost all electronic devices (and arranged in some randomly chosen blood splatters on the floor) was a spiral-shaped interference pattern. So in reality, for you, there is absolutely no connection between the two.

 

Again, sorry, I didn't do the thorough background checking that I should have.

[Xyph]

Ah, oops, I should apologize for my defensiveness, then - I assumed (a bit too quickly, it turns out) that you were being critical of asking about things from fictional science, but since that's not the case, sorry about my reaction.