Amino acids make up every protein. There are 20 total amino acids each with a unique side-chain group. Some additional amino acids are listed, but only 20 are coded from DNA directly. These side-chains allow for chemical interactions like sulfide bonds, hydrogen bonds, and ionic bonds. Amino acids are further divided by being non-polar, polar, and charged. They link together with a peptide bond making a string of amino acids a polypeptide. Finally, each amino acids is assigned a name, a three-letter symbol and a one-letter symbol.

Amino Acids are involved in many systems and issues with its breakdown can cause diseases:

• In the liver: major site of urea production in the urea cycle
• Alpha-keto acids can deliver amino groups to the liver
• Ammonium is toxic: lethargy, headache, vomiting, seizures, death
• Seen in compromised liver