DNA - How Many Strands?

[sophia8]

This, of course, has also affected our molecular structure, as our two strand DNA is being reconnected back to its original form. Some people say that we originally had a 13 strand DNA, some say more and some less. However, whenever another activation is added, the group evolves to the next level.

I came across the above extract in an online article, on a New Age site dealing with angels, the Mayan Prophecies, 2012 and suchlike.
I know this stuff about having more than two strands of DNA is total b*ll*cks, but can someone tell me (in simple words please!) just why it's b*ll*cks?

 

[Iconoclast]

I came across the above extract in an online article, on a New Age site dealing with angels, the Mayan Prophecies, 2012 and suchlike.
I know this stuff about having more than two strands of DNA is total b*ll*cks, but can someone tell me (in simple words please!) just why it's b*ll*cks?

Sorry Sophia, I can't help you with the question of why that article is bollocks, but I'm fairly sure that the "Perfect Being" from Luc Besson's movie "The Fifth Element" had 13 strands of DNA, perhaps that's where the site got it's information from.

And, I can't say I've ever heard a report of anyone ever finding DNA from any organism that had a number other than two strands.

 

[Matabiri]

I know this stuff about having more than two strands of DNA is total b*ll*cks, but can someone tell me (in simple words please!) just why it's b*ll*cks?

At the very least, we have two strands of DNA because one strand "locks" into the other, like a jigsaw. These two strands then coil around each other - hence double-helix.

Having an odd number of DNA strands makes no sense, and seeing as one strand can only interact with one other strand, having more than two is essentially the same as saying there's something special and unique about having two apples, rather than one.

 

[pgwenthold]

Re: Re: DNA - How Many Strands?

At the very least, we have two strands of DNA because one strand "locks" into the other, like a jigsaw. These two strands then coil around each other - hence double-helix.

Having an odd number of DNA strands makes no sense, and seeing as one strand can only interact with one other strand, having more than two is essentially the same as saying there's something special and unique about having two apples, rather than one.

On the contrary, people have observed triple stranded DNA, and it can be stable.

A recent example

J. Am. Chem. Soc. 2004, vol 126, p 70 - 71

 

[Dymanic]

It sounds like someone may have become confused by the fact that the DNA strand (in every cell, about six feet of it!) is distributed among distinct bodies, called chromosomes. These come in pairs, 23 of them in (normal) humans.

 

[geni]

The bits that hold the two strand of DNA together are the base pairs. There are four of these CATG they an only pair up with the right one (ie AT&CG). They bond through hydrogen bonding. This means that if we try to add a third (or more) strand of DNA there is no where for it to join on to sice all the places where hydrogen bonds could join are taken up by the pairing of the first two strands. (there is also the whole way DNA replicates ad the why tRNA is synthersysed and pretty much all of the biochemisty around DNA).

Eddited to accept correction in above post. The bit about the boichemistry still stands

 

[Prester John]

And, I can't say I've ever heard a report of anyone ever finding DNA from any organism that had a number other than two strands.

There are viruses that have a single strand of DNA for a genome (also single and double stranded RNA)

eg
H-1 parvovirus ssDNA virus
Poliovirus ssRNA virus

but i'm not aware of any organisms with more then 2 strands.

Maybe as suggested above, someone has got their chromosomes and DNA strands mixed up.

 

[pgwenthold]

The bits that hold the two strand of DNA together are the base pairs. There are four of these CATG they an only pair up with the right one (ie AT&CG). They bond through hydrogen bonding. This means that if we try to add a third (or more) strand of DNA there is no where for it to join on to sice all the places where hydrogen bonds could join are taken up by the pairing of the first two strands. (there is also the whole way DNA replicates ad the why tRNA is synthersysed and pretty much all of the biochemisty around DNA).

So why is there triple helix DNA, that actually has biological function?

Here is the abstract from a review (it's a chinese journal so I won't bother with the cite; see above for a recent study). The actual review is written in chinese, but I didn't feel like looking for an english version:

A review with 26 refs. The stability of triple helix DNA was discussed in terms of its endogenous and exogenous conditions such as chain length, base sequence, base modification, backbone structure of ODN and temp., pH, salt, ligand binding. Functions of triplex DNA include regulating genetic expression and transcription, protecting the DNA sequence from enzyme cleavage, serving as a mol. cleaver.

Here's a review in english

Guzzo-Pernell, N.; Lawlor, J. M.; Haralambidis, J. Triple helical DNA. Biomedical Peptides, Proteins & Nucleic Acids (1997), Volume Date 1996-1997, 2(4), 107-122

There's an awful lot more to DNA than just Watson-Crick base pairing and the double helix.

 

[geni]

Ok thats a new one.

 

[Rolfe]

Ok thats a new one.

I'll say! One wonders how it could possibly work, in about the same way as one wonders how a zip might be designed to join three edges!

This one always confuzzles me, because after you've got the simple double helix there's a lot more coiling and twisting before you get to the level of the chromosome structure. And after making a complete prat of myself in the "Colour of Blood" thread, I'm a bit wary.

But right enough, even if one might conceive of a three-way zip, I don't see how you could really have any more. And even the three-stranded idea - are they saying it actually occurs in nature?

The way the whole thing works is like a uniquely coded zip that, when open, can build its "other half" to specification. As Geni said, these are hydrogen bonds that take some powerful enzymes to unzip, and it's hard to see where anything else could be joined on - even that triple idea is boggling my mind.

Go to four, and you're just sayng that you have two double-helix strands in association with each other, I think, and so on. There are some very strange people around, though - thirteen is probably their lucky number.

Pretty piccies of double helix here.

Rolfe.

 

[Paul C. Anagnostopoulos]

People might be using the word strand loosely. Perhaps they are thinking of more than two instances of chromosomes, as happens with Down Syndrome.

Edited to add: Nah, it's way crazier than that.

~~ Paul

 

[athon]

As far as I'm aware, triple-helix nucleic acid has no possible biological functioning, as it is not a base-paired molecule. I do seem to recall reading this article, and on looking further into it this molecule, while being made of nucleic acid, bonds differently. I'd need to look it all up again.

The concept of more than one strand per molecule has been explored so often in science fiction that it is now almost cliche. As mentioned, Fifth Element is just one example. Afterall, how do you keep something familiar while making it alien? You give it similar DNA that has 'more' of the same.

Could you create a triple or higher nucleic acid polymer with information? Probably, but it would be superfluous at best. Afterall, we only have one strand that codes for anything - the other strand is an 'antisense' polymer that is there for proof-reading, and not much else. It does not carry extra coding information. So adding a third strand makes no biological sense.

Of course, we could always invent a reason. Sci-fi writers do that all the time.

Athon

 

[wayrad]

Afterall, we only have one strand that codes for anything - the other strand is an 'antisense' polymer that is there for proof-reading, and not much else. It does not carry extra coding information.

Hunh? Is it really that way in eukaryotes? My bugs have plenty of genes on both strands. With only one chromosome, they'd better make maximum use of it...

edit: Ah, I see, never mind. You didn't mean the entire strand was noncoding, just the part opposite the gene. Which strand is the noncoding one can vary from place to place.

 

[Matabiri]

Re: Re: Re: DNA - How Many Strands?

On the contrary, people have observed triple stranded DNA, and it can be stable.

A recent example

J. Am. Chem. Soc. 2004, vol 126, p 70 - 71

Well, now there's a thing.

Although, as Athon has mentioned, does it have a biological function? And if so, does it form a "higher being"? ;-)

 

[pgwenthold]

I'll say! One wonders how it could possibly work, in about the same way as one wonders how a zip might be designed to join three edges!

Who says they have to line up perfectly end to end? Don't restrict yourself to linear structures. Consider three segments, we'll call them AA, BB, and AB. If we require that an A half matches up with a B half, then you could create AA - BB. But you could also put the A part of AB against half of BB, the B part against half of AA, leaving a free A and B in AA and BB that can loop around and bind up (I hope you see what I am saying). Given the flexibility of DNA, these things can happen. Since it needs to coil and twist anyway, it can find more ways to do that.

But right enough, even if one might conceive of a three-way zip, I don't see how you could really have any more. And even the three-stranded idea - are they saying it actually occurs in nature?

See the abstract from the chinese review I posted above.

Functions of triplex DNA include regulating genetic expression and transcription, protecting the DNA sequence from enzyme cleavage, serving as a mol. cleaver.

The way the whole thing works is like a uniquely coded zip that, when open, can build its "other half" to specification. As Geni said, these are hydrogen bonds that take some powerful enzymes to unzip, and it's hard to see where anything else could be joined on - even that triple idea is boggling my mind.

Even regular double stranded DNA is much more complex than you are implying here. For example, the Watson-Crick helical structure is one of three low energy forms. It is the lowest energy form, usually, but there are some instances where the other structures are preferred, and even if they aren't, they certainly are accessed during the typical thermal motion of the complex.

Go to four, and you're just sayng that you have two double-helix strands in association with each other, I think, and so on. [/B]

Can be, but not necessarily. There can be more complicated structures.

Granted, this stuff we are talking about here is for the most part not standard undergraduate biochemistry (although, I have to admit, I never had biochem so I don't know) and is pretty advanced. I would think it would be fairly standard in introductory grad level biochem, though, although again I don't know.

 

[pgwenthold]

Re: Re: Re: Re: DNA - How Many Strands?

Well, now there's a thing.

Although, as Athon has mentioned, does it have a biological function? And if so, does it form a "higher being"? ;-)

I have not seen any indication of a triple helix based genome.

 

[Soapy Sam]

"I have not seen any indication of a triple helix based genome."

It's called a Mandelbrat. Lives as a parasite inside the trousers of the Bagooglian Bratwurstbeastii of wormhole VII

 

[Iconoclast]

It's called a Mandelbrat.

Mandelbrat.... damn, that'd be a pretty cool username.

 

[Jon_in_london]

Could you create a triple or higher nucleic acid polymer with information? Probably, but it would be superfluous at best. Afterall, we only have one strand that codes for anything - the other strand is an 'antisense' polymer that is there for proof-reading, and not much else.

Indeed my antipodean friend!

What TF would be the point in having 13 DNA strands? You only need one fuh chrisake! We have two because as Athon sez, it provides a degree of proofrreading. It also results in a more stable structure.

From the evolutionary point of view- imagine DNA is the hard-drive of a laptop that you have to carry around. It might make sense to carry a backed-up drive with you but who TF is going to cart around 13 backed-up copies!?? Now in the world of biology and survival of the fittest- you would be very fit if you had to waste vast amounts of time and energy copying a dozen odd redundant copies of your genome.

Having more (or one) strand will simply result in a structure thats either far too stable (dsRNA for eg. can be almost impossible to separate, even with boiling NaOH) or far too unstable.

BTW- I know of a FOUR-stranded DNA structure but it only serves as some kind of junction thingy and is transient in nature.

 

[Dymanic]

Or maybe they were thinking about polypoidy. The probable ancestral haploid number of the cotton plant, for example, is 13.