Short answers, pulled from the story.
Amino acids are organic compounds that contain both an amino group and a carboxylic acid functional group. The carbon next to the carboxyl group, called the alpha-carbon, also carries a hydrogen and a side chain unique to each amino acid.
Twenty-two alpha-amino acids are incorporated into proteins, and only these 22 appear in the genetic code of life. Of these, 20 are encoded directly by the universal genetic code, while selenocysteine and pyrrolysine are added through unique mechanisms.
Nine of the 20 standard amino acids are essential for humans: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. The human body cannot synthesize them at the level needed for normal growth, so they must be obtained from food.
The first amino acid, asparagine, was isolated in 1806 by the French chemists Louis-Nicolas Vauquelin and Pierre Jean Robiquet from asparagus. The last of the 20 common amino acids to be discovered was threonine, in 1935 by William Cumming Rose.
All chiral proteinogenic amino acids share the L configuration, meaning they are the left-handed enantiomers of the alpha-carbon. Glycine is the exception because its side chain is a hydrogen atom, making its alpha-carbon non-stereogenic.
A zwitterion is the form amino acids favor in water near neutral pH, with a deprotonated carboxyl group and a protonated amino group at the same time. It has a net charge of zero but contains both positive and negative sites, so describing it as uncharged is misleading.