Difference Between Hydrophobic and Hydrophilic Amino Acids

The key difference between hydrophobic and hydrophilic amino acids is that the hydrophobic amino acids are nonpolar whereas the hydrophilic amino acids are polar.

Amino acids are the building blocks of proteins. A protein is a giant polymer molecule which is an essential component of all living organisms. Furthermore, amino acids are mainly in two types as essential and nonessential amino acids. Moreover, we can categorize them as hydrophilic and hydrophobic amino acids, depending on their physicochemical nature. They are different from each other mainly based on the polarity.

CONTENTS

1. Overview and Key Difference
2. What are Hydrophobic Amino Acids
3. What are Hydrophilic Amino Acids
4. Side by Side Comparison – Hydrophobic vs Hydrophilic Amino Acids in Tabular Form
5. Summary

What are Hydrophobic Amino Acids?

Hydrophobic amino acids are a type of amino acids with a nonpolar nature. Likewise, the name “hydrophobic” derives because it does not interact with water (“hydro” – water). Water is a polar solvent. Since these amino acids are nonpolar, they cannot dissolve in water.

Hence, the hydrophobic nature of these compounds arises due to the side chains they have in their chemical structure. An amino acid has the general formula in which a central carbon atom is attached with a hydrogen atom, a carboxyl group, an amine group and a side group (R group). This R group can be simply an atom (hydrogen atom) or a long side chain. Thus, if the side chain is very long and consists mostly of carbon and hydrogen atoms, they are hydrophobic. Furthermore, they have small dipole moments. Therefore, they tend to repel from the water.

Moreover, the hydrophobic amino acids among essential amino acids are as follows.

• Glycine
• Alanine
• Valine
• Leucine
• Isoleucine
• Proline
• Phenylalanine
• Methionine
• Tryptophan

What are Hydrophilic Amino Acids?

Hydrophilic amino acids are a type of amino acids with a polar nature. The name “hydrophilic” derives because it attracts water. Since water is a polar solvent and these amino acids are also polar, they can dissolve in water.

Hydrophilic amino acids contain either short side chains or side chain with hydrophilic groups. Usually, these amino acids occur at the surface of protein molecules, and they have large dipole moments. Consequently, they tend to attract water.

Moreover, the major hydrophilic, essential amino acids are as follows:

• Serine
• Threonine
• Cysteine
• Asparagine
• Glutamine
• Tyrosine

What is the Difference Between Hydrophobic and Hydrophilic Amino Acids?

Hydrophobic amino acids are a type of amino acids which have a nonpolar nature while hydrophilic amino acids are a type of amino acids in which have a polar nature. Hence, this is the key difference between hydrophobic and hydrophilic amino acids. Moreover, hydrophobic amino acids have long side chains with mostly carbon and hydrogen atoms whereas hydrophilic amino acids have either short side chains or side chain with hydrophilic groups. As another important difference between hydrophobic and hydrophilic amino acids, hydrophobic ones occur at the centre of proteins while hydrophilic amino acids are on the surface.

The below illustration shows detailed description on the difference between hydrophobic and hydrophilic amino acids.

Summary – Hydrophobic vs Hydrophilic Amino Acids

In brief, amino acids are the building blocks of proteins. Moreover, according to the polarity, there are two types as hydrophilic and hydrophobic amino acids. The key difference between hydrophobic and hydrophilic amino acids is that the hydrophobic amino acids are nonpolar whereas the hydrophilic amino acids are polar.

Reference:

1. Reddy, Michael K. “Amino Acid.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 30 Oct. 2018. Available here  

Image Courtesy:

1.”Amino acids”By Dan Cojocar (CC BY-SA 3.0) via Commons Wikimedia  
2.”Serine simple”By Sten André – Own work, (Public Domain) via Commons Wikimedia