Cysteine is a hydrophobic amino acid with a thiol group on its side chain due to the presence of a sulphur atom.
This amino acid is found in many foods such as broccoli, garlic, eggs and wheat germ.
Cysteine is synthesized from other amino acids, including methionine and serine. Cysteine is therefore not classified as an essential amino acid because the human body is capable of producing it. Vitamin B6 is also involved in its synthesis.
Cysteine is an amino acid used in the composition of proteins such as keratin, which is present in nails and hair.