Link Reaction?? HELP!!

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

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

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 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?

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?

My mistake, I assumed we were still talking about oxidative decarboxylation. For normal decarboxylation, the organic product is ethanal.

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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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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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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