Removal of amino group of amino acid to transform into keto acid is

In oxidative deamination, amino groups are removed from amino acids, resulting in the formation of corresponding keto acids and ammonia. Ammonia is toxic nitrogenous waste and so is converted to urea by ornithine cycle in the liver.  Urea is less toxic and is eliminated by the kidneys.

Transamination is a chemical process in which transfer of an amino group from one amino acid takes place and that amino group is transferred to the keto group of a keto acid. 

Nitrification is the process by which ammonia is converted to nitrites (NO₂^-) and then nitrates (NO₃^-). 

Ammonification is the process where microbes like bacteria break down nitrogen-containing chemicals from detritus, into simple substances like ammonia.