Crystals of the amino acid histidine

A microscopic exploration of crystals in daily life substances. Transmitted light and polarizing filters are used to provide coloration to transparent crystals in the amino acid Cysteine (Cys, C). Cysteine is a non-essential amino acid, which means that it is biosynthesized in humans. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid. The thiol side chain often participates in enzymatic reactions, serving as a nucleophile. The thiol is susceptible to oxidization to give the disulfide derivative cystine, which serves an important structural role in many proteins.