BRAINCAKEProtein Homeostasis in the Liver
The body cannot store excess amino acids. Dietary proteins are digested to amino acids, which are used to make new proteins. Any amino acids that are not needed are broken down in the liver, so that the energy in them can be used and their nitrogen safely removed.
Deamination is the removal of the amine group (−NH2) from an amino acid. In liver cells the amine group is removed as ammonia (NH3), leaving a keto acid. The keto acid can be respired, via the Krebs cycle, or converted into glucose, glycogen or fat for storage.
Ammonia is very soluble and highly toxic: it raises the pH of cells and interferes with enzymes and nerve function. So the liver immediately combines it with carbon dioxide in the ornithine cycle to make urea, which is much less toxic:
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All 41 lessons in Homeostasis · All Edexcel A-level Biology topics