Cambridge O Level Biology · Syllabus 5090 · Excretion
Deamination
What is Deamination?
The removal of the nitrogen-containing part of amino acids, which takes place in the liver and results in the formation of urea. Deamination is the body's response to an excess of amino acids, which cannot be stored as amino acids: the nitrogen-containing part is removed and converted into urea, a soluble nitrogen-containing waste that passes into the blood plasma and is later removed by the kidneys, while the remaining carbon-containing part is used in other reactions of the body. Deamination happens in the liver, never in the kidney.
This definition is part of the Excretion chapter in Cambridge O Level Biology.
Common mistakes with Deamination
- “The kidneys make urea.” Why wrong It puts manufacture and removal in the same organ, which destroys the whole liver–kidney structure of the topic. Say instead The liver makes urea by deamination; the kidneys remove it from the blood.
- “Deamination happens in the kidneys.” Why wrong Deamination is a chemical process carried out by the liver. The kidney filters and reabsorbs; it does not break down amino acids. Say instead Deamination is the removal of the nitrogen-containing part of amino acids, in the liver.
- “Deamination is how protein is digested.” Why wrong Digestion happens in the alimentary canal and produces amino acids. Deamination happens in the liver and disposes of the ones there is no use for. Different place, different molecule, opposite purpose. Say instead Protein is digested to amino acids; excess amino acids are later deaminated in the liver.
Examiner tips on Deamination
- Two words that must not be swapped. Deamination happens to amino acids that are already inside the body, in the liver. Digestion happens to protein inside the alimentary canal, and produces amino acids in the first place. Digestion supplies the raw material; deamination disposes of the surplus. A candidate who writes “deamination digests the protein” has merged two processes that happen in different places, to different molecules, for opposite reasons.
Questions students ask about Deamination
Where is urea made, and where is it removed?
Urea is made in the liver, by deamination of excess amino acids. It is removed from the blood by the kidneys and leaves the body dissolved in urine. The two organs must not be interchanged: the liver never excretes urea and the kidney never manufactures it.
What is deamination?
Deamination is the removal of the nitrogen-containing part of amino acids, which takes place in the liver and results in the formation of urea. It is necessary because excess amino acids cannot be stored as amino acids. The remaining carbon-containing part is used in other reactions of the body.