What is the Difference Between Serine and Threonine

The main difference between serine and threonine is that serine contains a hydroxyl group in the β carbon whereas threonine contains a methyl group and a hydroxyl group in the β carbon.

Serine and threonine are two types of hydroxyl-containing amino acids that contain an α-amino group. Generally, serine is a non-essential amino acid, and threonine is an essential amino acid.  

Key Areas Covered

1. What is Serine
     – Definition, Structure, Function
2. What is Threonine
     – Definition, Structure, Function
3. Similarities Between Serine and Threonine
     – Outline of Common Features
4. Difference Between Serine and Threonine
     – Comparison of Key Differences

Key Terms

Serine, Threonine

What is Serine

Serine is an α-amino acid that is important in the biosynthesis of proteins. Structurally, serine contains an amine group in the α-carbon along with a carboxyl group and a side chain of hydroxymethyl group. Furthermore, serine is a polar amino acid. It is also a non-essential amino acid synthesized under physiological conditions inside the body. The metabolites that synthesize serine include glycine. The l-stereoisomeric form is the naturally-occurring form of serine. Normally, the oxidation of 3-phosphoglycerate involves the biosynthesis of serine.

Figure 1: Serine

Furthermore, lamb, eggs, edamame, liver, pork, sardines, salmon, seaweed, and tofu are the food that contains the L form of serine. Generally, the codons that encode serine are UCU, UCC, UCA, UCG, AGU, and AGC. Serine is important for the metabolism of purines and pyrimidines. It also serves as a precursor to several amino acids, including glycine, tryptophan, and cysteine. In addition to that, serine serves as a precursor to a number of metabolites, such as folate and sphingolipids.  

What is Threonine

Threonine is another α-amino acid important in the biosynthesis of proteins. Generally, threonine is a polar, uncharged amino acid. Therefore, it contains an amino group, a carboxyl group, and a side chain containing a hydroxyl group. Threonine is an essential amino acid that cannot be synthesized inside the body. Threonine is synthesized from the aspartate. The codons that encode threonine include ACU, ACC, ACA, and ACG.

Figure 2: Threonine

Moreover, threonine is susceptible to numerous posttranslational modifications, such as O-linked glycosylation and phosphorylation. It also converts into pyruvate by the action of the enzyme threonine dehydrogenase. Poultry, cottage cheese, fish, meat, lentils, black turtle bean, and sesame seeds are food rich in threonine. In general, threonine contains side chains that undergo hydrogen bonding with serine, forming ST motifs, ST turns, and ST staples.     

Similarities Between Serine and Threonine

• Serine and threonine are two types of α-amino acids that contain hydroxyl groups.
• Both are hydrophilic amino acids.

Difference Between Serine and Threonine

Definition

Serine refers to a hydrophilic amino acid, a constituent of most proteins, while threonine refers to a hydrophilic amino acid, an essential amino acid.

Codons

The codons that encode serine are UCU, UCC, UCA, UCG, AGU, and AGC, while the codons that encode threonine include ACU, ACC, ACA, and ACG.

Essential Amino Acids

Serine is a non-essential amino acid, while threonine is an essential amino acid.

Side Groups

Serine contains a hydroxyl group in the β carbon, while threonine contains a methyl group and a hydroxyl group in the β carbon.

Synthesis

Moreover, serine is synthesized from glycine, while threonine is synthesized from aspartate.

Function

Serine participates in the metabolism of purines and pyrimidines, while threonine converts to pyruvate.

Occurrence

Serine occurs in lamb, eggs, edamame, liver, pork, sardines, salmon, seaweed, and tofu, while threonine occurs in poultry, cottage cheese, fish, meat, lentils, black turtle bean, and sesame seeds.

Conclusion                                                      

In brief, serine and threonine are two types of amino acids hydrophilic amino acids. Both are α-amino acids that contain hydroxyl groups. Generally, serine is a non-essential amino acid that contains a hydroxyl group in the β carbon. Serine is synthesized from glycine. Generally, serine participates in the metabolism of purines and pyrimidines. In comparison, threonine is an essential amino acid that contains a methyl group and a hydroxyl group in the β carbon. In addition to that, threonine is synthesized from aspartate. However, threonine converts into pyruvate. Therefore, the main difference between serine and threonine is their structure and function.      

References:                

1. “Amino acids – threonine.” Biology Arizona Edu. 

Image Courtesy:

1. “L-Serin – L-Serine” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia
2. “Threonin – L-Threonine” By NEUROtiker – Own Work (Public Domain) via Commons Wikimedia