What is the Difference Between Serine and Threonine

The key difference between serine and threonine is that serine is a non-essential amino acid that contains an α amino group, a carboxyl group, and a side chain consisting of a hydroxymethyl group, while threonine is an essential amino acid that contains an α amino group, a carboxyl group, and a side chain consisting of a hydroxyl group.

Amino acids are the precursors to make complex proteins. They are organic compounds containing amino (NH₃⁺) carboxyl (COO^–) functional groups. There are four main amino acids classes based on polarity. They are amino acids with non-polar side chains (tryptophan), amino acids with uncharged polar side chains (serine, threonine), amino acids with polar negatively charged side chains (aspartic acid), and amino acids with polar positive charged side chains (lysine). Serine and threonine are two amino acids with uncharged polar side chains.

CONTENTS

1. Overview and Key Difference
2. What is Serine  
3. What is Threonine
4. Similarities – Serine and Threonine
4. Serine vs Threonine in Tabular Format
5. Summary – Serine vs Threonine

What is Serine?

Serine is an amino acid that contains an α-amino group, a carboxyl group, and a side chain consisting of a hydroxymethyl group. It is an amino acid with an uncharged polar side chain. Therefore, it is classified as a polar amino acid. It can be synthesized in the human body under normal physiological conditions. This makes it a non-essential amino acid. It is usually encoded by codons UCU, UCC, UCA, UCG, AGU, and AGC in the genetic code. This organic compound is one of the naturally occurring proteinogenic amino acids. It was first obtained from silk protein in 1865 by Emil Cramer. Food sources rich in L stereoisomer of serine are eggs, lamb, liver, edamame, tofu, pork sardines, seaweed, etc. Industrially, serine can be produced from glycine and methanol catalyzed by the enzyme hydroxymethyltransferase.

Serine has numerous biological functions. It participates in the biosynthesis of purines and pyrimidines. Serine also plays an important role in the catalytic function of many enzymes such as chymotrypsin and trypsin. Furthermore, D-serine is a signalling molecule in the brain. Serine deficiency leads to disorders such as severe neurological symptoms like congenital microcephaly, severe psychomotor retardation. The deficiency of serine can also cause intractable seizures.

What is Threonine?

Threonine is an amino acid that contains an α-amino group, a carboxyl group, and a side chain consisting of the hydroxyl group. It is also an amino acid with an uncharged polar side chain. It is an essential amino acid for humans since it cannot be synthesized in the human body under normal physiological conditions. It must be obtained from the diet. Threonine is synthesized from aspartate in bacteria E.coli. It is encoded by the codons ACU, ACC, ACA, and ACG in the genetic code. This amino acid was first discovered by William Cumming Rose and Curtis Mayer in 1936. Adult humans require threonine about 20 mg/kg body weight per day. The food rich in threonine includes cottage cheese, poultry, fish, meat, lentils, black turtle bean, and sesame seeds.

Threonine fulfils different biological functions. It is an important component of gastrointestinal mucin. Threonine is also a nutritional modulator of the intestinal immune system via complex signalling networks. Moreover, threonine dehydratase deficiency can cause non-ketotic hyperglycinaemia. Threonine deficiency can also cause neurologic dysfunction and lameness.

What are the Similarities Between Serine and Threonine?

• Serine and threonine are two amino acids with uncharged polar side chains.
• Both are proteinogenic amino acids.
• They form small motifs such as ST turns, ST motif, and ST staples by interacting with each other.
• Deficiency of both leads to neurologic disorders.

What is the Difference Between Serine and Threonine?

Serine is a non-essential amino acid composed of an α-amino group, a carboxyl group and a side chain consisting of a hydroxymethyl group, while threonine is an essential amino acid composed of an α-amino group, a carboxyl group and a side chain consisting of the hydroxyl group. So, this is the key difference between serine and threonine. Furthermore, serine is encoded by codons UCU, UCC, UCA, UCG, AGU and AGC in the genetic code, while threonine is encoded by ACU, ACC, ACA and ACG in the genetic code.

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

Summary – Serine vs Threonine

Serine and threonine are two proteinogenic amino acids. They are also two amino acids with uncharged polar side chains. Serine is a non-essential amino acid composed of an α-amino group, a carboxyl group and a side chain containing a hydroxymethyl group, while threonine is an essential amino acid composed of an α-amino group, a carboxyl group and a side chain containing a hydroxyl group. Thus, this is the key difference between serine and threonine.

Reference:

1. “Serine.” An Overview | ScienceDirect Topics.
2. “Threonine: Overview, Uses, Side Effects, Precautions, Interactions, Dosing and Reviews.” WebMD.

Image Courtesy:

1. “Serine” (CC BY-SA 3.0) via Commons Wikimedia

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