Cysteine is a naturally occurring amino acid, serving as a fundamental building block for proteins within the human body and other organisms. It is one of the 20 standard amino acids that compose proteins. A distinguishing feature of cysteine is its unique sulfur-containing side chain, known as a thiol or sulfhydryl group (-SH). This chemical group is responsible for many of cysteine’s biological roles.
Molecular Weight of Cysteine
The molecular weight of cysteine is approximately 121.16 grams per mole (g/mol) or 121.16 Daltons (Da). Molecular weight represents the sum of the atomic weights of all atoms that make up a molecule. For cysteine, its weight is derived from its chemical formula, C₃H₇NO₂S, indicating that each molecule contains three carbon atoms, seven hydrogen atoms, one nitrogen atom, two oxygen atoms, and one sulfur atom. The sulfur atom within cysteine’s structure contributes significantly to its overall mass.
Significance of Cysteine
Cysteine’s unique thiol group contributes to its diverse and important biological functions. One of its most recognized roles is the formation of disulfide bonds, which occur when the sulfur atoms of two cysteine molecules link together. These strong covalent bonds stabilize the three-dimensional structures of many proteins, influencing their shape and function. For instance, disulfide bonds are present in antibodies, contributing to the stability of their antigen-binding sites, and in enzymes, where they help stabilize the active site for catalytic activity.
Beyond structural integrity, cysteine is a precursor for glutathione, often called the body’s primary antioxidant. Glutathione, a tripeptide composed of glutamate, cysteine, and glycine, plays a significant role in protecting cells from oxidative stress by neutralizing harmful free radicals and aiding in detoxification processes within the liver. Supplemental forms of cysteine, such as N-acetylcysteine (NAC), are often used to increase glutathione levels, supporting the body’s antioxidant defense mechanisms.
Cysteine is also involved in various metabolic pathways, including the transsulfuration pathway, where it can be synthesized from methionine. It is a precursor for other sulfur-containing molecules like taurine and plays a part in the production of hydrogen sulfide, a signaling molecule. Due to these wide-ranging roles, dysregulation of cysteine metabolism has been linked to various health conditions, including certain amino acid disorders, cardiovascular disease, and neurological disorders such as Alzheimer’s and Parkinson’s.