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Will all proteins fall apart by exaggerated heat?

  1. Apr 14, 2013 #1
    Like the topic; if you boil proteins (or vitamines for that matter), will the molecular structure break?
    For example warm milk etc.
     
  2. jcsd
  3. Apr 14, 2013 #2

    mfb

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    With sufficient temperature, all chemical bonds break apart. Even before that happens, proteins can change their shape. I would expect that boiling water at atmospheric pressure is sufficient for most proteins to get modified in some way.
     
  4. Apr 14, 2013 #3
    You might be interested in a process called denaturation.


    http://en.wikipedia.org/wiki/Denaturation_%28biochemistry%29

     
  5. Apr 14, 2013 #4
    There are many levels of structure in a protein. Your question is not really specific enough.

    Heat will denature proteins, meaning there will be enough thermal motion to overcome the H-bonds stabilizing things like helices and sheets and how they are arranged in space etc (referred to as secondary and tertiary structure). There are other interactions of proteins which are more resistant to just heat. For instance when running SDS-PAGE gels, you denature proteins with heat but add some type of reducing agent such as dithiothreitol of mercaptoethanol in order to reduce disulfide bridges which are covalent and fairly stable to heat. Note we are talking reasonable temperatures here, say up to 100 degrees C. Throwing a protein into the sun will yield a different outcome than in a boiling water bath.

    Other covalent bonds in proteins are even more stable to physical and chemical perturbations. For instance the peptide bond is so strong that if you want to digest a protein without using peptidases, you boil it for hours and hours in 6M HCl and then hope you have fully digested the protein. There are yet other covalent bonds such as C-C bonds etc, which are pretty much stable to anything you can throw at them short of combustion or some such thing.

    So the proteins in milk don't necessarily "fall apart" upon heating or boiling, but they may denature or rearrange to a different configuration from the native one. It really comes down to what you mean when you say fall apart. Perhaps you may be more specific with your question, because "fall apart" can be interpreted in many different ways.
     
  6. Apr 14, 2013 #5
    Thanks alot for your informative answers. Yes, well we have all heard about "can I boil this without the nutrients breaking up" etc. Sorry for not being especially specific. I suppose I meant boiling in water more exactly.
     
  7. Apr 14, 2013 #6
    Thanks alot Yanick. Even though I read about this at school at the moment, I didn't really understand all of what you wrote here but I'll try to understand. :) Thx! Very appreciated
     
  8. Apr 14, 2013 #7
    Sorry if I used language that may be a bit over your head.

    Here's the takeaway from what I wrote above. I presented my argument somewhat from a top down approach, here it is from a bottom up approach.

    atoms -> molecules/amino acids -> peptides -> proteins -> multi-peptide proteins.

    The last three exhibit extra levels of organization such as primary, secondary, tertiary and quaternary structure. Briefly, primary structure of a protein is simply just the sequence of amino acids read in a particular direction. Secondary structure refers to how the "string" will arrange itself into things like helices, turns, loops, sheets etc. Tertiary refers to how the secondary structure elements are arranged in space. Finally quaternary structure refers to how two different (or identical) proteins arrange themselves in space if they happen to interact with one another.

    Basically you're question is vague because "falling apart" can mean going from a protein, say hemoglobin (which displays all 4 levels of protein structure), to just atoms of C, H, N, O, S etc.

    Something like heat denaturation can go all the way to unwinding the protein where it loses its secondary through quaternary structure but still remains a chain of amino acids. You can go further and start cutting up the "string" into individual amino acids (or shorter strings of amino acids), this takes more than just a bit of boiling as you must break peptide (AKA amide) bonds which are pretty strong bonds. Typically this requires something like an enzyme which cuts peptides up known as a peptidase or very harsh conditions such as boiling in concentrated acid for a long time.

    You can also go on to say, I want to break each individual amino acid up into smaller molecules, this takes much more effort because bonds like C-C, C-H etc are extremely strong and stable. You can still do something like breaking a protein down where your products are not amino acids but even smaller molecules by combusting (burning) proteins. In that scenario you'll go from proteins to CO2, H2O, N2, SO2 etc. You can even go further and try to get everything into just C, H, N etc, but that would require even harsher conditions and I don't even know how to give an example of something like that.

    Hope that helps. In regards to people mentioning boiling away micro/macronutrients there are a few things to consider as well. Vitamins are not the same proteins. When boiling things in water, the water soluble vitamins and other nutrients will come out of the cell and go into solution in the water. Then, unless you are drinking the water you boiled stuff in, you will have lost all those nutrients. So there is a bit of truth to that.

    When it comes to denaturing proteins, its important to remember that your stomach environment is highly acidic, something like a pH of 2. Most proteins will in fact denature in your stomach. In addition there are enzymes in your intestines which will cut the protein up to make it suitable for transport into blood and throughout the body. Huge proteins are broken down anyway into the amino acids or short peptides of a few amino acids. So the people who talk about denatured dietary proteins being bad for you are a little off their rocker IMO.

    Hope this helps.
     
  9. Apr 15, 2013 #8
    That's is very interesting and fairly understandable for me. Thx :)
     
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