Excretion

What happens amino acids in excess to immediate requirements

• They are respired to ensure that little is wasted as the molecules are a store of energy

• Excess amino acids are carried to the liver in the blood plasma

• Here they are absorbed by hepatocytes

What is the first stage of what happens to amino acids in the liver

Deamination

Describe deamination (3)

• amino acid is oxidised by an enzyme catalyst

• Amine group and a hydrogen atom are removed from the main structure of the amino acids

• The amine group is reduced to ammonia by the addition of the hydrogen atom

What happens to the non-nitrogenous portion of the deaminated amino acids

Can be respired, or converted to carbohydrate or lipid

What is the stage after deamination to get rid of ammonia

The urea cycle

Describe what happens to the ammonia during the urea cycle

• enzymes in the liver cells catalyse the reaction of carbon dioxide with the ammonia

• The less toxic nitrogenous compound, urea, is produced alongside water

• CO2 + 2NH3 → CO(NH2)2 + H2O

What other nitrogenous excretory products can be produced other than urea

Uric acid or creatinine

How is urea excreted

• urea and water are released from the liver cells to the bloodstream and transported to the kidneys through hepatic portal veins

• The blood is filtered in the kidneys

• Urea is a small and very soluble molecule, so it is easily passed out by the kidneys as a solution in the water (urine)