Our bodies require 20 different amino acids to accomplish all it needs to do for us to live. Together, these amino acids are sequenced and folded to combine in almost endless ways. The resulting proteins are used to build our muscles, bones, hair, and nails, but that is only the beginning. They make enzymes that facilitate the myriad chemical reactions in our bodies. They carry nutrients and other necessary molecules though our blood and across cell membranes. They carry signals from one part of the body to another. Antibodies are proteins. The tasks of proteins are almost too many to count.
Of the 20 amino acids we need, our bodies can make 11 of them. The other 9 we must get through our diets -- they are called the essential amino acids, because it is essential that we eat them. The amount we need of each of the amino acids is different -- for example, according to the standards of the World Health Organization, a person who weighs 70 kg. (154 lbs.) needs only 280 mg of tryptophan daily, but 2100 mg of lysine and 2730 mg of leucine.
It is said that an egg has almost the perfect balance of the essential amino acids we need, and animal proteins in general have ample amounts of all of them. Plant sources of amino acids include legumes, grains, nuts, and seeds, but any one of them on their own doesn't have "balanced" amounts of all of the amino acids (with the possible exception of quinoa). Therefore, people who are relying on plant foods for proteins can ensure adequate amounts by eating a variety of these foods - beans and rice, for example, is a classic combination which has the full range of essential amino acids.
The essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
The other amino acids we need (that our bodies can make) are: alanine, asparagine, aspartic acid, cystein, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.