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    So half of the books say, oh pyruvate is first oxidised and the decarboxylated forming acetate. one states:

    Pyruvate is decarboxylated (loses a carbon atom in form of co2). Pyruvate is oxidised, forming acetate and nad is reduced. coa is combined with acetate to give acetyl coA.

    Now here's the problem, how can a molecule be decarboxylated then the same pyruvate be oxidised, makes no sense!!

    Now i was learning anaerobic respiration , and it said in alcoholic fermentation, pyruvate is decarboxylated to ethanal which is reduced to ethanol (makes sense).

    So applying same principal, if the pyruvate is decarboxylated in link reaction, do we get ethanal, then isn't this ethanal which get oxidised and then is turned into ethanoic acid (acetic acid) which is then fixed with coA to form acetyl coA.

    I've google this so much but nobody mentions ethanal??? Someone please explain this to me the correct way
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    What I say is don't overcomplicate it.
    Anaerobic respiration is a two step process in which pyruvate is only decarboxylated and then its the ethanal which is reduced to ethanol.
    In the link reaction the pyruvate molecule is oxidised and decarboxylated so its a completely different reaction to anaerobic respiration. There is no comparison to it.

    Hope it makes sense
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    (Original post by Hajra Momoniat)
    What I say is don't overcomplicate it.
    Anaerobic respiration is a two step process in which pyruvate is only decarboxylated and then its the ethanal which is reduced to ethanol.
    In the link reaction the pyruvate molecule is oxidised and decarboxylated so its a completely different reaction to anaerobic respiration. There is no comparison to it.

    Hope it makes sense
    "In the link reaction the pyruvate molecule is oxidised and decarboxylated so its a completely different reaction to anaerobic respiration."

    But what i'm saying is pyruvate can't be oxidised first and then decarboxylated, it's the other way around.
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    It doesn't matter what order you say in the exam as long as you say pyruvate is oxidised and decarboxylated into acetate then youll be fine
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    (Original post by Hajra Momoniat)
    It doesn't matter what order you say in the exam as long as you say pyruvate is oxidised and decarboxylated into acetate then youll be fine
    ah right thanks
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    (Original post by Asad_2015)
    So half of the books say, oh pyruvate is first oxidised and the decarboxylated forming acetate. one states:

    Pyruvate is decarboxylated (loses a carbon atom in form of co2). Pyruvate is oxidised, forming acetate and nad is reduced. coa is combined with acetate to give acetyl coA.

    Now here's the problem, how can a molecule be decarboxylated then the same pyruvate be oxidised, makes no sense!!

    Now i was learning anaerobic respiration , and it said in alcoholic fermentation, pyruvate is decarboxylated to ethanal which is reduced to ethanol (makes sense).

    So applying same principal, if the pyruvate is decarboxylated in link reaction, do we get ethanal, then isn't this ethanal which get oxidised and then is turned into ethanoic acid (acetic acid) which is then fixed with coA to form acetyl coA.

    I've google this so much but nobody mentions ethanal??? Someone please explain this to me the correct way
    Pyruvate is a keto acid, so the bit that gets removed via decarboxylation is the carboxylic acid part, but there's also a lone pair which can be removed by oxidation to produce the acetyl group minus one electron

    It's not called ethanal before oxidation because the carbon that has the oxygen is a radical with only three bonds and a lone electron pair - with one more hydrogen it would be either of them.

    I'd recommend looking at the structures of pyruvate, ethanoate (acetate), ethanoyl (acetyl) and ethanol + ethanal
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    (Original post by h3rmit)
    Pyruvate is a hydroxy acid, so the bit that gets removed via decarboxylation is the carboxylic acid part, but there's also a hydroxyl leftwhich can be oxidised to produce the radical acetyl group

    It's not called ethanal after oxidation (or ethanol before oxidation) because the carbon that has the hydroxyl is a radical with only three bonds and an unpaired electron - with one more hydrogen it would be either of them.

    I'd recommend looking at the structures of pyruvate, ethanoate (acetate), ethanoyl (acetyl) and ethanol + ethanal
    so isnt decarboxylated pyruvate, ethanal?
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    (Original post by Asad_2015)
    so isnt decarboxylated pyruvate, ethanal?
    No, because the organic product of pyruvate decarboxylation is lacking one of the hydrogens that would make it ethanal (C2H4O)
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    (Original post by h3rmit)
    No, because the organic product of pyruvate decarboxylation is lacking one of the hydrogens that would make it ethanal (C2H4O)
    the how in anaerobic respiration is pyruvate decarboxylated to form ethanal?
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    (Original post by Asad_2015)
    the how in anaerobic respiration is pyruvate decarboxylated to form ethanal?
    My mistake, I assumed we were still talking about oxidative decarboxylation. For normal decarboxylation, the organic product is ethanal.
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    (Original post by h3rmit)
    My mistake, I assumed we were still talking about oxidative decarboxylation. For normal decarboxylation, the organic product is ethanal.
    So what link reaction is different, but anaerobic is reductive decarboxylation??


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    (Original post by h3rmit)
    My mistake, I assumed we were still talking about oxidative decarboxylation. For normal decarboxylation, the organic product is ethanal.
    Also let's say Pyruvate is decarboxylayed we get ethanal, oxidising ethanal gives ur a carboxylic acid ethanoic acid which is acetic acid ???


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    (Original post by Asad_2015)
    So what link reaction is different, but anaerobic is reductive decarboxylation??


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    When a molecule is split as in decarboxylation, it's hard to say whether it's oxidative or reductive. I'd say it's reductive, as the carbon (in the pyruvate) that was bonded to the carboxyl has that bond replaced by a hydrogen

    (Original post by Asad_2015)
    Also let's say Pyruvate is decarboxylayed we get ethanal, oxidising ethanal gives ur a carboxylic acid ethanoic acid which is acetic acid ???


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    Not if you consider oxidation in terms of hydrogens. A hydrogen is removed in oxidative decarboxylation (dehydrogenative decarboxylation or something like that might be more apt).
    Ultimately, pyruvate dehydrogenase is a large, complicated, enzyme complex, and how things actually work is too in depth for A2.
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    (Original post by h3rmit)
    When a molecule is split as in decarboxylation, it's hard to say whether it's oxidative or reductive. I'd say it's reductive, as the carbon (in the pyruvate) that was bonded to the carboxyl has that bond replaced by a hydrogen


    Not if you consider oxidation in terms of hydrogens. A hydrogen is removed in oxidative decarboxylation (dehydrogenative decarboxylation or something like that might be more apt).
    Ultimately, pyruvate dehydrogenase is a large, complicated, enzyme complex, and how things actually work is too in depth for A2.
    So in exam would it be fine to say:

    Pyruvate is decarboxylated. Pyruvate is oxidised, forming acetate.


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    (Original post by Asad_2015)
    So in exam would it be fine to say:

    Pyruvate is decarboxylated. Pyruvate is oxidised, forming acetate.


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    When I said think of oxidation in terms of hydrogens, I meant hydrogens are lost to make it oxidation, so the oxidation isn't the same as you'd do in organic chem with refluxing - so you don't form ethanoate, you form the acetyl
 
 
 
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