What is the Difference Between Acidic and Basic Amino Acids

The main difference between acidic and basic amino acids is that the acidic amino acids contain acidic side chains at the neutral pH whereas the basic amino acids contain basic side chains at the neutral pH. Furthermore, the side chain of the acidic amino acid contains carboxylic acid groups while the side chain of the basic amino acids contains amino groups. 

Acidic, basic, and neutral amino acids are the three types of amino acids characterized based on their polarity of the side chain or the organic R group. Generally, an amino acid contains an amino group (-NH2), carboxylic group (-COOH), an organic R group, and a hydrogen atom attached to a central carbon atom. 

Key Areas Covered 

1. What are Acidic Amino Acids
     – Definition, Side Chain, Importance
2. What are Basic Amino Acids
     – Definition, Side Chain, Importance
3. What are the Similarities Between Acidic and Basic Amino Acids
     – Outline of Common Features
4. What is the Difference Between Acidic and Basic Amino Acids
     – Comparison of Key Differences

Key Terms 

Acidic Amino Acids, Amino Groups, Basic Amino Acids, Carboxylic Acid Groups, Polarity

What are Acidic Amino Acids 

Acidic amino acids are a type of polar amino acids which contain carboxylic groups (-COOH) in their side chains. That means; these amino acids contain two carboxylic groups in the amino acid structure: one carboxylic group in the side chain and the other attached to the central carbon atom. Thus, this decreases the pKa in a solution. Therefore, acidic amino acids can lose protons from their carboxylic groups in the side chains to produce an acidic solution.

Figure 1: Properties of Amino Acids

The two main types of acidic amino acids are glutamic acid and aspartic acid. 

What are Basic Amino Acids 

Basic amino acids are the other type of polar amino acids. They contain an amino group (-NH2) in their side chain. Here also, basic amino acids contain two amino groups. One amino group occurs in the side chain while the second one is attached to the central carbon atom. On the contrary to acidic amino acids, basic amino acids, therefore, consist of a high pKa. Thus, this allows obtaining protons to the amino group in the side chain, producing a basic solution.  

Figure 2: Interactions between Acidic and Basic Amino Acids

The three types of basic amino acids are lysine, arginine, and ornithine. 

Similarities Between Acidic and Basic Amino Acids 

• Acidic and basic amino acids are two types of amino acids characterized based on the properties of the organic R group. 
• The organic R group consists of different polarities in these amino acids.  
• The hydrogen bonds between acidic and basic amino acids are important during the formation of beta sheets.  
• Also, these amino acids join protein subunits together to form the tertiary structure of proteins.  
• Furthermore, both types of amino acids serve as catalytic sites, stabilizing various metabolites and acidic or basic intermediates during the enzymatic catalysis of biological reactions. Moreover, they stabilize the hydrolysis of ATP by serving as a secondary binding site.  

Difference Between Acidic and Basic Amino Acids 

Definition 

Acidic amino acids refer to an amino acid with a second acid moiety while basic amino acids refer to an amino acid containing a second basic group (usually an amino group). 

Side Chain/Organic R Group 

A major difference between acidic and basic amino acids is that acidic amino acids contain acidic side chains at the neutral pH while basic amino acids contain basic side chains at the neutral pH.  

Side Chain Components 

The side chain of the acidic amino acids contains carboxylic acid groups (-COOH) while the side chain of the basic amino acids contains amino groups (-NH2).  Thus, this is another difference between acidic and basic amino acids.

pKa 

Furthermore, acidic amino acids consist of low pKa values, which allow losing protons while basic amino acids consist of high pKa values, which allow them to bind protons. 

Charge 

Their charge is also a difference between acidic and basic amino acids. Acidic amino acids bear a negative charge in their side chain while basic amino acids bear a positive charge in their side chain.  

Examples 

Some acidic amino acids are glutamic acid and aspartic acid while the three types of basic amino acids are lysine, arginine, and ornithine. 

Conclusion 

Acidic amino acids contain carboxylic groups in their side chain, allowing them to bear a negative charge. On the other hand, basic amino acids contain amino groups in their side chain, allowing to bear a positive charge. These charges on both acidic and basic amino acids are important in the formation of secondary structures of proteins. They are important during the enzymatic catalysis of biochemical reactions as well. Therefore, the main difference between acidic and basic amino acids is the type of functional groups present in their side chains.   

Reference:

1. Ophardt, Charles E. “Characteristics and Properties of Amino Acids.” VERTUAL CHEMBOOK, 2003, Available Here

Image Courtesy:

1. “Amino Acids” By Dancojocari – Own workPrint It HereThis W3C-unspecified vector image was created with Adobe Illustrator.iThe source code of this SVG is valid. (CC BY-SA 3.0) via Commons Wikimedia  
2. “Next Revisit Glutamic Acid Lysine salt bridge” By Chem540f09grp6 – Own work (Public Domain) via Commons Wikimedia