Production of Urea
- Many metabolic reactions within the body produce waste products
- The removal of these waste products is known as excretion
- Many excretory products are formed in humans, with two in particular (carbon dioxide and urea) being formed in much greater quantities than others
Urea
- Urea is produced in the liver
- It is produced from excess amino acids
- If more protein is eaten than is required, the excess cannot be stored in the body
- However, the amino acids within the protein can still provide useful energy
- To make this energy accessible, the amino group is removed from each amino acid
- This process is known as deamination:
- The amino group (-NH2) of an amino acid is removed, together with an extra hydrogen atom
- These combine to form ammonia (NH3)
- The remaining keto acid may enter the Krebs cycle to be respired, be converted to glucose, or converted to glycogen / fat for storage
Deamination of an amino acid
- Ammonia is a very soluble and highly toxic compound that is produced during deamination; it can be very damaging if allowed to build up in the blood
- It dissolves in the blood to form alkaline ammonium hydroxide, disrupting blood pH
- It can impact the reactions of cell metabolism such as respiration
- It interferes with cell signalling processes
- This is avoided by converting ammonia to urea
- Urea is less soluble and less toxic than ammonia
- Ammonia is combined with carbon dioxide to form urea
Formation of urea
