TBR O-Chem/Bio Discrepancy?

[coyotelime]

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TBR O-Chem clearly said that anabolism = synthesis = reduction, examples include gluconeogenesis, fatty acid synthesis, and generally took place in the cytosol (Section 6, O-Chem book 2), and that catabolism = breaking down = oxidation, examples include glycolysis, generally took place in the matrix (except glycolysis).

But in a bio passage about insulin receptors, they ask what kind of wash should be used to break a disulfide bond(dimer). In the explanation, they say that breaking the S-S bond requires a reducing wash. Using their oxidation state definitions this makes sense. Either S in a S-S bond would have an oxidation state of 0(ignoring the other bonds' oxidation state contributions), and breaking that bond would add 1H each to the S, so the S-H would give S an oxidation state that is 1 less than before because S is more electronegative than H.

Am I missing something really basic here? Thanks.

Edit: Is there a difference between breaking down a molecule and breaking bonds? Also, as a general rule, I can just look at the oxidation state to make sure if it's oxidized/reduced correct?

 

[Catburr]

TBR O-Chem clearly said that anabolism = synthesis = reduction, examples include gluconeogenesis, fatty acid synthesis, and generally took place in the cytosol (Section 6, O-Chem book 2), and that catabolism = breaking down = oxidation, examples include glycolysis, generally took place in the matrix (except glycolysis).

I'm not sure if ALL anabolic reactions are reductive for the thing being built. Might be a generalization, might not. I can't think of an example of reductive catabolism or oxidative anabolism, but that doesn't mean it doesn't exist.

But in a bio passage about insulin receptors, they ask what kind of wash should be used to break a disulfide bond(dimer). In the explanation, they say that breaking the S-S bond requires a reducing wash. Using their oxidation state definitions this makes sense. Either S in a S-S bond would have an oxidation state of 0(ignoring the other bonds' oxidation state contributions), and breaking that bond would add 1H each to the S, so the S-H would give S an oxidation state that is 1 less than before because S is more electronegative than H.

When disulfide bonds break in a reducing solution, a hydrogen (or some reagent) is added to each sulfur, yup. Common example of this is adding beta-mercaptoethanol to your protein before you run it through an SDS-PAGE gel: cysteine-S--S-cysteine + 2 HOCH2CH2SH → 2 cysteine-SH + HOCH2CH2S-SCH2CH2OH

A bond is breaking, but bonds are forming too, so you can still think of that as reduction = bond formation, or, reduction = loss of oxygen or gain of hydrogen.

Edit: Is there a difference between breaking down a molecule and breaking bonds? Also, as a general rule, I can just look at the oxidation state to make sure if it's oxidized/reduced correct?

If a passage talks about breaking down a molecule, bonds are being broken, yeah. I can't think of anything else they'd be talking about. Change in oxidation state is one way to see if oxidation/reduction occurred. You can look for gain/loss of oxygen/hydrogen too, although that obviously doesn't work if those molecules aren't present. It does work for the reduction of disulfide bonds, as an example.

 

[coyotelime]

I'm not sure if ALL anabolic reactions are reductive for the thing being built. Might be a generalization, might not. I can't think of an example of reductive catabolism or oxidative anabolism, but that doesn't mean it doesn't exist.



When disulfide bonds break in a reducing solution, a hydrogen (or some reagent) is added to each sulfur, yup. Common example of this is adding beta-mercaptoethanol to your protein before you run it through an SDS-PAGE gel: cysteine-S--S-cysteine + 2 HOCH2CH2SH → 2 cysteine-SH + HOCH2CH2S-SCH2CH2OH

A bond is breaking, but bonds are forming too, so you can still think of that as reduction = bond formation, or, reduction = loss of oxygen or gain of hydrogen.



If a passage talks about breaking down a molecule, bonds are being broken, yeah. I can't think of anything else they'd be talking about. Change in oxidation state is one way to see if oxidation/reduction occurred. You can look for gain/loss of oxygen/hydrogen too, although that obviously doesn't work if those molecules aren't present. It does work for the reduction of disulfide bonds, as an example.

Okay. As a general rule I think I will just use oxidation states from now on to be safe. Thanks for your help!