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Author Topic: Why doesn't water denature proteins?  (Read 9651 times)

Offline cryonicfry

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Why doesn't water denature proteins?
« on: 20/04/2010 16:46:36 »
Hi
Why doesn't water denature proteins?
Protein denaturation by ethanol is explained by the formation of hydrogen bonds between the ethanol and certain aminoacids which breaks those normally formed between two aminoacids so why isn't the same possible for water?
(I even considered the hydrophobicity of proteins…proteins are hydrophobic because they are -mostly- apolar and water is polar…..but the same can be said about ethanol…it is polar -less than water but still polar-).
Amino acid side chains are said to be directed towards the inside of the molecule (protein) in order to limit interactions with water.....if so why doesn't it limit alcohol denaturation?

All answers are greatly appreciated but please provide a source when you can.
« Last Edit: 23/04/2010 16:10:34 by BenV »


 

Offline daveshorts

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Re: Why doesn't water denature proteins?
« Reply #1 on: 21/04/2010 19:02:45 »
I have no sources and am a physicist and so probably wrong, but I would have through that water has a very similar (if not stronger) effect than ethanol, just the proteins are 'designed' to be their correct conformation when dissolved in water. If cells had evolved dissolved in ethanol, then adding water would be a lethal thing to do to their proteins.
 

Offline cryonicfry

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Re: Why doesn't water denature proteins?
« Reply #2 on: 22/04/2010 08:07:44 »
The thing is, if protein conformation is all there is to it I think ethanol would have the same effect as water (it wouldn't do anything).
My current hypothesis is that since Ethanol's dipole moment= 1.69 Debye and Water's dipole moment= 1.85 Debye  ethanol is slightly less polar and can penetrate to the interior of a protein and have a denaturing effect......... :-\ :-\ :-\ :-\ :-\ :-\ :-\ seems a bit far fetched...
 

Offline Bored chemist

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Re: Why doesn't water denature proteins?
« Reply #3 on: 22/04/2010 22:04:08 »
There are several sorts of interactions. Since the dipole moments are similar the dipole interactions might be the same, but the hydrogen bonding would be different because the ethyl bit would get in the way.
 

Offline rosy

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Re: Why doesn't water denature proteins?
« Reply #4 on: 23/04/2010 12:30:44 »
Proteins depend heavily on "hydrophobic" interactions (a misnomer, but nevertheless the name in common usage).
Water molecules like to form strong hydrogen bonds with each other, if there's a large surface area of protein in the solution, these interactions are disrupted. In order to minimise exposed surface area, the bits of the protein which aren't able to interact with each other tend to fold over themselves to minimise exposed surface area.

It's basically the same reason oil and water don't mix.

In ethanol, however, the tendancy for non-interacting regions to stick together is much weaker so proteins tend to unfold.
 

Offline cryonicfry

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Why doesn't water denature proteins?
« Reply #5 on: 27/04/2010 19:13:39 »
Proteins depend heavily on "hydrophobic" interactions (a misnomer, but nevertheless the name in common usage).
Water molecules like to form strong hydrogen bonds with each other, if there's a large surface area of protein in the solution, these interactions are disrupted. In order to minimise exposed surface area, the bits of the protein which aren't able to interact with each other tend to fold over themselves to minimise exposed surface area.

It's basically the same reason oil and water don't mix.

In ethanol, however, the tendency for non-interacting regions to stick together is much weaker so proteins tend to unfold.
I still have one problem :
Absolute ethanol is less effective against bacteria than a mixture of ethanol and water (70% ethanol).This is explained by the fact that absolute ethanol denatures protein too quickly and forms a thin outer layer of denatured protein beyond which the cell lives on....
If water is supposed to make proteins fold in a hydrophobic manner why is a mixture of water and ethanol more potent than pure ethanol?
 

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Why doesn't water denature proteins?
« Reply #5 on: 27/04/2010 19:13:39 »

 

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