The first step in catabolizing, or breaking down, an amino acid is the removal of its amine group (-NH3). Amine groups can be transferred or removed through transamination or deamination, respectively.
Transamination is the transfer of an amine group from an amino acid to a keto acid (amino acid without an amine group), thus creating a new amino acid and keto acid as shown below.
Figure 6.411 Generic transamination reaction where the top keto acid is converted to an amino acid, while the bottom amino acid is converted to a keto acid1
Keto acids and/or carbon skeletons are what remains after amino acids have had their nitrogen group removed by deamination or transamination. Transamination is used to synthesize nonessential amino acids.
Deamination is the removal of the amine group as ammonia (NH3), as shown below.
Figure 6.412 Deamination of cytosine to uracil (nucleotides, not amino acids)2
The potential problem with deamination is that too much ammonia is toxic, causing a condition known as hyperammonemia. The symptoms of this condition are shown in the following figure.
Figure 6.413 Symptoms of Hyperammonemia3
Our body has a method to safely package ammonia in a less toxic form to be excreted. This safer compound is urea, which is produced by the liver using 2 molecules of ammonia (NH3) and 1 molecule of carbon dioxide (CO2). Most urea is then secreted from the liver and incorporated into urine in the kidney to be excreted from the body, as shown below.
Figure 6.414 Production of urea helps to safely remove ammonia from the body4-6