The basic building blocks of protein are amino acids, organic compounds that contain the chemical subunits known as an amino group and a carboxyl group. To form proteins, amino acids bond to one another with a special chemical bond known as a peptide bond.
There are 20 different amino acids used to create proteins in living organisms. All organisms on earth use the same amino acids. These amino acids each have two versions that are mirror images of each other, but those used by living organisms are always what is known as "left-handed." When amino acids form outside of living organisms, the numbers of each type of mirror image molecule are approximately equal. In humans, amino acids fall into three categories: essential amino acids, nonessential amino acids and conditional amino acids.
The human body can assemble nonessential amino acids from suitable materials. It can also assemble conditional amino acids under ideal conditions, but under certain stresses the body's ability to construct them is diminished. The human body cannot create essential amino acids from raw materials on its own and can only get them via consuming food. All of the amino acids are vital for the construction of proteins, which are in turn vital for both building the body and making it work.