The biochemistry of nitrogen compounds foreshadows the complex analysis of protein chemistry. Generally there are three great classes of proteins: the proteins that occur naturally (albumin, globulin, protamins etc.), the conjugated proteins, that is, combinations of proteins with other substances (nucleoproteins, glycoproteins, phosphoproteins, chromoproteins or lipoproteins); and the derived proteins, formed from the hydrolysis of a protein molecule (metaproteins, peptone, coagulated proteins etc.). Some enzymes contain also nitrogen.

The "nitrogen fixation" is the name of any process where the free nitrogen combines with other elements, originating the nitrogen compounds. This "fixation" can be made chemically or through certain bacteria, as the azotobacter chroococcum and clostridium pasteurianum. In the natural processes of "nitrogen fixation" there are a cooperative action between bacteria and certain plants as the peas, the beans or the clover.

The nitrogen cycle foreshadows that the animals obtain the nitrogen through the ingestion of proteins, either animal or vegetable. The plants synthesize its proteins from the inorganic compositions of the soil. They can also absorb free nitrogen from atmosphere through some existent bacteria in the soils.

When the animals are exposed to high atmospheric pressures, there is a considerable portion of nitrogen that is dissolved in the blood or in another fluids of the body. If the pressure decreases drastically, the nitrogen dissolved form small bubbles, that wandering freely in the corporal liquids can cause paralyses, fainting, pains in muscles and articulations and, eventually, death. These symptoms can be avoided with a slow decompression.

In the living organisms, the usual concentration of nitrogen is 16%, while its natural abundance is of about 0,3 parts in 1000.