What is the Difference Between Cysteine and Serine?

Cysteine and serine are both proteinogenic amino acids, meaning they are important structural components in proteins. The key difference between cysteine and serine lies in the presence of a sulfur atom in cysteine, which replaces the oxygen atom in serine. Here are some differences between cysteine and serine:

1. Sulfur content: Cysteine is a sulfur-containing amino acid, while serine is not.
2. Chemical structure: Cysteine has a thiol group (-SH) in place of the hydroxyl group (-OH) in serine.
3. Acidity: The thiol group in cysteine makes it more acidic than serine. For example, the pKa value of the carboxyl group in cysteine is 1.96, while in serine it is 2.1.
4. Physical properties: Although cysteine and serine have similar bond lengths and angles due to the minor difference in atomic size, their physicochemical properties are quite different.
5. Function: Cysteine is known for its ability to form CYS-CYS disulfide bridges, which are a major structural feature of proteins. It is also a target for covalent (irreversible) inhibition and plays a key role in stabilizing extracellular proteins. Serine, on the other hand, is involved in the metabolism of purines and pyrimidines, catalytic function in many enzymes, as a constituent in proteins, as a signaling component, and in gustatory sensation.

Despite their similarities, cysteine and serine have distinct chemical and physical properties that contribute to their different functions in proteins.

Comparative Table: Cysteine vs Serine

Cysteine and serine are both proteinogenic amino acids, meaning they are important structural components in proteins. However, they have some key differences: