Difference Between Acidic and Basic Amino Acids

Key Difference – Acidic vs Basic Amino Acids
 

Amino acids are the building blocks of proteins. A chain of amino acids is known as a polypeptide and the combination of several polypeptide chains form a protein molecule. The key difference between acidic and basic amino acids is that acidic amino acids have acidic side chains whereas basic amino acids have basic side chains at neutral pH.

An amino acid molecule has four parts; a carboxylic acid group, an amine group, a hydrogen atom and “R” (alkyl) group. These four groups are directly bonded to a central carbon atom. The “R” group is known as a side chain in an amino acid.

CONTENTS

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

What are Acidic Amino Acids?

Acidic amino acids are polar amino acids having a negative charge at the neutral pH. This negative charge occurs in the side group (R group) of the amino acid. These side chains contain carboxylic acid groups other than the carboxylic acid group directly bound to the central carbon atom. These side chains are known as acidic side chains because these negative charges are created due to the loss of protons (hydrogen ions) from the carboxylic groups in the side chain. Among the 20 essential amino acids, two amino acids are acidic amino acids; aspartate and glutamate.

The pKa of these two amino acids are low enough to lose a proton at the neutral pH and become negatively charged. (The pKa is a measure of the acid strength of an acid; smaller the pKa, higher the acidity. Therefore, compounds having low pKa values readily release protons).

Acidic amino acids are known to activate the central nervous system of human body. Aspartate and glutamate are important excitatory neurotransmitters in the mammalian central nervous system.

What are Basic Amino Acids?

Basic amino acids are polar amino acids having a positive charge at the neutral pH. These amino acids have basic side chains (R groups). This basicity arises due to the presence of amine groups in the side chain (other than the amine group directly bonded to the central carbon atom).

There are three basic amino acids among 20 essential amino acids; arginine, lysine and histidine. The side chains of these amino acids contain many nitrogen atoms indicating the presence of many amine groups. Amine group are basic. Hence, they cause the basicity of amino acid molecule. The pKa of these amino acids is high enough to accept protons. The amine groups in the side chain readily bind protons. This binding of extra protons gives the amino acid molecule a net positive charge since protons are positively charged.

What is the Difference Between Acidic and Basic Amino Acids?

Summary –Acidic vs Basic Amino Acids

Amino acids are small molecules that undergo polymerization to form protein molecules. There are two main types of amino acids as acidic amino acids and basic amino acids. The difference between acidic and basic amino acids is that acidic amino acids have acidic side chains whereas basic amino acids have basic side chains at neutral pH.

Reference:

1.“Acidic Amino Acids.” Acidic Amino Acids – an Overview | ScienceDirect Topics. Available here 
2.“Amino Acids .” Nature News, Nature Publishing Group. Available here 
3.“Biomolecules:Protein 1.” Acidic and Basic Amino Acids. Available here

Image Courtesy:

1.’Aspartate (DMA)’By D.Azani – Own work, (CC BY-SA 4.0) via Commons Wikimedia  (Modified)
2.’L-Glutamat(2-) – L-glutamate(2-)’By ChemPro – Own work using: BKChem, (Public Domain) via Commons Wikimedia  (Modified)