What is the Difference Between Cysteine and Serine

The key difference between cysteine and serine is that cysteine is a sulfur-containing amino acid while serine is not a sulfur-containing amino acid.

Cysteine and serine are proteinogenic amino acids, meaning these amino acids are important structural components in proteins. Cysteine and serine chemical structures differ from each other according to a single atom where cysteine contains an oxygen atom in the -OH group while serine contains a sulfur atom instead of the oxygen atom.

1. Overview and Key Difference
2. What is Cysteine
3. What is Serine
4. Cysteine vs Serine in Tabular Form
5. Summary – Cysteine vs Serine

What is Cysteine?

Cysteine is an amino acid that is semi-essential for our body, and it has the chemical formula HOOC-CH-(NH₂)-CH₂SH. It is a type of proteinogenic amino acid. It has a thiol side chain that often participates in enzymatic reactions in the form of a nucleophile. This thiol group is subjected to oxidation, forming the disulfide derivative of the cysteine molecule. This disulfide derivative plays an important role in many proteins as structural components. Moreover, cysteine is useful as a food additive (the E number is E920).

Figure 01: The Chemical Structure of Cysteine Molecule

When isolated, cysteine appears as white crystals or powder that is water-soluble. Similar to most other amino acids, cysteine also occurs as a zwitterion. Moreover, this compound shows chirality where L-cysteine is more common than D isomer.

We can find cysteine and its derivatives in food. For example, cysteinyl can be found in high protein foods. Although we name it as a semi-essential amino acid, it is essential for infants, elderly people, and people having certain metabolic disorders. If a sufficient amount of methionine is present in the body, the body can make enough cysteine by itself. Some of the biological functions of cysteine include acting as a precursor for the antioxidant glutathione, as a precursor to iron-sulfur clusters, in metal ion binding, role in protein structure, etc.

What is Serine?

Serine is an alpha-amino acid having the chemical formula C3H7NO3. It is important in the biosynthesis of proteins. This compound contains an alpha-amino group and a side chain containing a hydroxymethyl group. This side group makes the amino acid a polar amino acid. It is considered a non-essential amino acid because the body can synthesize it normally. The codons that can encode this amino acid include UCU, UCC, UCA, UCG, AGU, and AGC.

Serine is a naturally occurring proteinogenic amino acid. However, the L isomer of serine is the most common form. Glycine and some other metabolites can produce this amino acid inside the body; therefore, it is not essential to take serine from the outside. When isolated, serine appears as white crystals or a white powder.

Cysteine and Serine - Side by Side Comparison

Figure 02: The Industrial Production Route for Serine

There are several important biological functions of serine, which include the use of serine in the metabolism of purines and pyrimidines, catalytic function in many enzymes, as a constituent in proteins, as a signalling component, gustatory sensation, etc.

What is the Difference Between Cysteine and Serine?

Cysteine and serine are proteinogenic amino acids. The key difference between cysteine and serine is that cysteine is a sulfur-containing amino acid while serine is not a sulfur-containing amino acid. Also, they have slightly different chemical structures where there is a -OH group in cysteine in the place of -SH group in serine.

The following infographic lists the differences between cysteine and serine in tabular form for side by side comparison.

Summary – Cysteine vs Serine

Cysteine and serine are proteinogenic amino acids, meaning these amino acids are important structural components in proteins. The key difference between cysteine and serine is that cysteine is a sulfur-containing amino acid while serine is not a sulfur-containing amino acid.

Reference:

1. “Cysteine.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine.

Image Courtesy:

1. “L-Cystein – L-Cysteine” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “Synthesis of dl-serine” By “dl-Serine”. Org. Synth. 20: 81; Coll. Vol. 3: 774. (Public Domain) via Commons Wikimedia