BRAINCAKERespiration of Proteins
Proteins are respired only when carbohydrate and lipid stores are low, for example during prolonged starvation. They are first hydrolysed by protease enzymes into amino acids.
Amino acids cannot be respired directly, because they contain nitrogen in their amine group (NH2). In mammals, excess amino acids are deaminated in the liver: the amine group is removed and forms ammonia. Ammonia is very toxic, so it is converted into urea in the ornithine cycle and excreted by the kidneys.
The part of the amino acid that remains is a keto acid (an organic acid). Depending on the amino acid, the keto acid is converted into:
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Key terms in this lesson
- keto acid
- The organic acid that remains after the amine group is removed from an amino acid during deamination.
More in Respiration
- Anaerobic Respiration - Plants and Microorganisms.
- Anaerobic Respiration - Mammals
- Respiratory Substrates
- Energy Values of Carbohydrates, Lipids and Proteins
- Respiration of Lipids
- Respiratory Quotient
- Calculating RQ
- Measuring RQ with a Respirometer
All 19 lessons in Respiration · All OCR A-level Biology topics