13. Amino acid metabolism; the fate of the carbon skeleton

Last updated on November 19, 2018 at 17:16


  • You should, in theory, know what amino acids are ketogenic, which are glucogenic and which are both
  • Important cofactors are biotin, THF and adoMet
  • D-amino acid oxidase detoxifies ingested D-amino acids
  • The carbon skeleton of degraded amino acids can be fumarate, succinyl-CoA, α-ketoglutarate, oxaloacetate, glutamate, pyruvate, acetyl-CoA and acetoacetyl-CoA
  • The degradation of branched-chain amino acid does not occur in the liver


You should learn and know the MRTs related to this (obviously). According to the lecturers, you should know what the carbon skeleton of each amino acid is degraded to (pyruvate or fumarate, for example). However, if you ask me, that’s too much work for maybe 4 points on the exam. I’d skip it. However, there are some things you can learn from this lecture.

There are three cofactors that are used in reactions related to this. They are biotin, tetrahydrofolate (THF), and adoMet. They all transfer chemical groups containing 1 carbon, but they transfer different groups.

Biotin transfers -COO groups, which is basically CO2, and is the most oxidized one-carbon group.

THF transfers either methylene (CH=CH) or methyl (CH3) groups.

AdoMet transfers only methyl groups, the most reduced and therefore highest energy.

All amino acids have two forms, the L and the D form. The L form is the one that our body uses and is composed of. They are drawn with the amino-group to the left. However, the D form also exists. This is drawn with the amino-group to the right. These amino acids cannot be used, and are degraded in the kidney by D-amino acid oxidase.

The degradation of the three branched-chain amino acids (valine, isoleucine, leucine), do not occur in the liver. That is because the liver lacks branched-chain aminotransferase, which is mostly found in muscle and brain.

This is the figure that you should know. I skipped it completely.


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12. Urea cycle

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14. Synthesis of non-essential amino acids

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