What makes the DNA Double Helix Possible

[Navin]

Homework Statement

The Reason for the Double helical Structure of DNA is the operation of -

A) Van Der Waals Forces

B)Dipole Dipole Interactions

C)Hydrogen Bonding

D)Electrostatic Attraction

2. Background of question

This question ,is part into the home work asignment my chem tracher gave me.
(Note : we were taught a great amount of DNA in Biology ,so we havequite a good background for attempting the question)

The Attempt at a Solution

My opinion

Now firstly i believe the answer should be Van Der Waals forces because without it, the DNA double helix won't be stable

Answer given -
Hydrogen bonding

My counter
Granted that Hydrogen bonding makes it possible for DNA to have 2 strands,but i am under the impression that it is Van Der waals forces give DNA the helical structure and not Hydrogen bonding alone.(atleast that's what i have been taught)

Am i wrong ?
Or Is the book wrong ?
https://en.m.wikipedia.org/wiki/DNA

https://science.howstuffworks.com/life/cellular-microscopic/dna1.htm

http://faculty.washington.edu/trawets/vc/theory/dna/index.html

 

[jedishrfu]

Its got to be the hydrogen bonds:

https://www.quora.com/Why-is-the-DNA-structure-a-double-helix

As you can see in the images of the above reference the bonds align the molecules and they then form the structure.

In your How Stuff Works reference under hydrogen bonds it talks about how they stabilize the structure.

 

[Borek]

Tricky. I would say the correct answer is D, in the end all bonding is about electrostatic attraction, and somehow I doubt you can say there is a single reason for the molecule shape, all kinds of interactions work together.

 

[jedishrfu]

Tricky. I would say the correct answer is D, in the end all bonding is about electrostatic attraction, and somehow I doubt you can say there is a single reason for the molecule shape, all kinds of interactions work together.

Chek out the quora discussion and images shown it seems to show clearly that its hydrogen bonding that does the trick. It seems that the electrostatic bonding is perhaps too general an answer.

However, I defer to your expertise. Thanks for commenting.

 

[Navin]

Its got to be the hydrogen bonds:

https://www.quora.com/Why-is-the-DNA-structure-a-double-helix

As you can see in the images of the above reference the bonds align the molecules and they then form the structure.

In your How Stuff Works reference under hydrogen bonds it talks about how they stabilize the structure.

Thanks For the reply Jidishrfu and Borek

Okay i have gone through the quora discussion and i still don't think its Hydrogwn bonding because it still doesn't explain the double helical structure. I mean one can have Hydrogen bonding without any double helix (for example beta pleated secandory structure of proteins )

And then again i can't fully dis agree with that as Hydrogen bonding is nescessaru for two oposite nitrogenous bases of nucleotides to bond.

(A beta pleated sheeth)

 

[Navin]

W

Tricky. I would say the correct answer is D, in the end all bonding is about electrostatic attraction.

Well i agree with Jedishfru that (D) is a bit general and i tgink they wa t a more specefic answer

However

I doubt you can say there is a single reason for the molecule shape, all kinds of interactions work together.

This is true...i mean after all , the double helical structure is an outcome of various forces .we can broadly say just one. Plus we also have hydrophobic interactions which come into play (spoken greatly about in the quora discussion)...so yea...frankly the answer should be( A ) (C) and (D)

 

[Borek]

I am afraid it can be one of those questions asked with a simple answer on mind, but without a second thought.

 

[jedishrfu]

You may be over thinking this. Molecules are held together by electron bonding. In the dna case multiple bonds fix the orientation of a given molecular component and thus the geometry of the larger molecule. These bonds are hydrogen bonds so that’s why I think it’s the answer.

 

[Bystander]

I am afraid it can be one of those questions asked with a simple answer on mind, but without a second thought.

..., and without the inclusion of the logically "correct" answer, "ribonucleic acids."

 

[Ygggdrasil]

At a simplistic level, most biologists think that it's the hydrogen bonds between the bases that allow DNA to form a double helix. The real answer is a bit more complicated. For example, see this argument in a review from Eric Kool at Stanford:

To a first approximation, hydrogen bonding between two gr oups in water is not energetically favorable because roughly equivalent hydrogen bonds to water must be exchanged for one such new bond. Thus, in enthalpic terms, solvation effects will not favor a hydrogen bonded pairing of two nucleobases. The bases G and C must first lose several hydrogen bonds to water in order to form a triply-hydrogen bonded pair. In addition, the bases lose entropy of relative translation and rotation in order to form the complex, a destabilizing effect. However, other entropic effects favor this pairing: The entropy of the freed water molecules is likely to be favorable; moreover, the formation of the second and third H-bond in the base pair comes with little additional translational/rotational entropy penalty. This is also true as multiple pairs are formed between two strands. Thus, the hydrogen bonding in a pair does appear to be energetically favorable in the context of a larger double helix.

https://www.annualreviews.org/doi/full/10.1146/annurev.biophys.30.1.1

Rather than hydrogen bonding, the stability of the DNA double helix comes largely from the base stacking interactions that form when adjacent bases align during the formation of the double helix (see the review cited above for more discussion). A set of key experiments testing this hypothesis were performed by Kool's group in the 1990s, where they synthesized DNA base analogs that lacked hydrogen bonding capability, but could form base pairs in DNA with similar selectivity and stability as natural nucleoside bases.

Here's a good summary from the conclusion section of the review cited above:

In general, recent data with DNA alone (in the absence of enzymes) suggests that hydrogen bonds contribute strongly to the selectivity of DNA base pairing in DNA alone. The bonds also appear to contribute to pairing energetics favorably, although with only moderate magnitude. It is possible to design nonhydrogen-bonded pairs that are somewhat selective and that are at least as stable as natural base pairs. From the steric standpoint, it appears that steric effects may affect base pairing preferences somewhat, though the influence may be moderate. Finally, stacking effects are probably the major influence of base pair stability and are the major force holding the double helix together.

 

[Navin]

At a simplistic level, most biologists think that it's the hydrogen bonds between the bases that allow DNA to form a double helix. The real answer is a bit more complicated. For example, see this argument in a review from Eric Kool at Stanford:

https://www.annualreviews.org/doi/full/10.1146/annurev.biophys.30.1.1

Rather than hydrogen bonding, the stability of the DNA double helix comes largely from the base stacking interactions that form when adjacent bases align during the formation of the double helix (see the review cited above for more discussion). A set of key experiments testing this hypothesis were performed by Kool's group in the 1990s, where they synthesized DNA base analogs that lacked hydrogen bonding capability, but could form base pairs in DNA with similar selectivity and stability as natural nucleoside bases.

Here's a good summary from the conclusion section of the review cited above:

Wow ! Another twist to the tale !

But yea this above cited article makes quite a bit of sence.

 

[Navin]

Anyways guys but the answer to the question is well...Hydrogen bonds.

Yup Jidishfru was right all along.

I asked my bio professor about this (and trust me when i say he is a perfectionist)

And he said the most relevant answer to this would be Hydrogen bonding.

The reason being that although vander waals forces and hydrophobic interactions play an extremely imortant role ,without hydrogen bonding ,it would never have been possible for the two strands to come to gether and no helix would be formed in the first place.

The main requirement;the basic requirement is ofcource rwo strands bought together and Hydrogen bonding does this.

Hence the most relevant option in the above give options is Hydrogen bonding.

Good job jefishfru...u were right.
If u answered the "N.E.E.T " exam paper you would get 4 marks.

 

[jedishrfu]

Yeah, thanks.

This is the sadness of schooling sometimes you need to answer according to the level of the course as your teacher will think you're smart-a** or that you got your facts wrong. In science, new discoveries sometimes take a long time before they enter the science books of public school. Sometimes what's considered fact today is not tomorrow. And then there's Texas, evolution, politics and how books are crafted but I digress.

I guess that's why I liked math so much, things were pretty well settled 300 years ago and the teachers continue teaching the works of Euclid, Pythagoras, Al-kwarizmi, and others. Your answers were provably right vs English where your grade was based on some arcane rules of proper writing that only the teacher knew. (my impression - I wrote red-marked papers, hanging participles, incredibly long sentences and incredibly short paragraphs with lame conclusions ;-) )

 

[Ygggdrasil]

Anyways guys but the answer to the question is well...Hydrogen bonds.

Yup Jidishfru was right all along.

I asked my bio professor about this (and trust me when i say he is a perfectionist)

And he said the most relevant answer to this would be Hydrogen bonding.

The reason being that although vander waals forces and hydrophobic interactions play an extremely imortant role ,without hydrogen bonding ,it would never have been possible for the two strands to come to gether and no helix would be formed in the first place.

The main requirement;the basic requirement is ofcource rwo strands bought together and Hydrogen bonding does this.

Hence the most relevant option in the above give options is Hydrogen bonding.

Good job jefishfru...u were right.
If u answered the "N.E.E.T " exam paper you would get 4 marks.

I'd point your professor to the review article I posted above and see if it changes his opinion.

 

[Navin]

I'd point your professor to the review article I posted above and see if it changes his opinion.

Ill give him the link to the article,it will be really fun to debate about this with him

But * according to the options* given he said H-- bonding was the most relevant

 

[jedishrfu]

Sometimes teachers are tough to convince but if you have a good working relationship with him/her and respect his/her expertise then you should be okay. Also it may come down to the level of the course and that h-bonds is the best simple answer for now.

 

[Navin]

Sometimes teachers are tough to convince but if you have a good working relationship with him/her and respect his/her expertise then you should be okay. Also it may come down to the level of the course and that h-bonds is the best simple answer for now.

Nah this Teacher is AWESOME and i have a superb working relation with him ,
But I am sure its down to the course level and for that level Hydrogen bonding is the perfect answer.

Anyway thanks so much for your help Jedishrfy
Borak and Ygggdrasil
Twas real kindness !