Production of Urea (Cambridge International A-Level Biology)

Spec point — 14.1.3 · state that urea is produced in the liver from the deamination of excess amino acids

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

The deamination of an amino acid chemical formulae

• 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 much less toxic than ammonia, so it can be safely transported in the blood to the kidneys

• Ammonia is combined with carbon dioxide to form urea

The formation of urea chemical formulae