The key difference between amino acid and imino acid is that an amino acid contains an amino group and a carboxylic group together in the same molecule whereas an imino acid contains an imino group and a carboxylic group together.
Although the terms amino acid and imino acid sounds similar, they are two different terms we use to name two different compounds. An amino acid is the building block of proteins. Imino acids are also related to amino acids since we can convert an amino acid into an imino acid.
CONTENTS
1. Overview and Key Difference
2. What is Amino Acid
3. What is Imino Acid
4. Side by Side Comparison – Amino Acid vs Imino Acid in Tabular Form
5. Summary
What is Amino Acid?
An amino acid is an organic molecule which acts as the building block of proteins. It essentially contains an amine group (-NH2), carboxylic group (-COOH), alkyl group (-R) and a hydrogen atom (-H) attached to the same central carbon atom. Therefore, the chemical elements in an amino acid are carbon, hydrogen, oxygen, and nitrogen. Sometimes, there is sulfur as well.
Figure 01: Different Amino Acids
If the amine group and carboxylic group of the amino acid are attached to the first carbon atom of the carbon chain, we call it an alpha amino acid. Often, the term amino acid refers to alpha amino acids since they are abundant. There are 22 amino acids involved in protein formation. We call them “proteinogenic amino acids”.
Among them, nine proteinogenic amino acids are essential amino acids for us because our body cannot produce it. Therefore, we need to take them from outside, i.e. food sources. Other amino acids can be produced in our body; thus, there is no need to take them from outside.
What is Imino Acid?
An imino acid is an organic compound containing an imino group and a carboxylic group together. We can denote imine group as (>C=NH). Therefore, unlike in amino acids, these molecules have a double bond between carbon and nitrogen atoms.
Figure 02: Imine Group Attached to Carbon
Some enzymes can convert amino acids into imino acids. For instance, D-amino acid oxidase enzymes are such enzymes. Moreover, proline contains a secondary amine group (we call it an imine), instead of a primary amine group. Hence, we call proline an “imino acid”.
What is the Difference Between Amino Acid and Imino Acid?
An amino acid is an organic molecule which acts as the building block for proteins while an imino acid is an organic molecule having an imine group. Hence, the key difference between amino acid and imino acid is that an amino acid contains an amino group and a carboxylic group together in the same molecule whereas an imino acid contains an imino group and a carboxylic group together.
Moreover, the chemical bond between the central carbon atom and the nitrogen atom of amino group in amino acids is a single bond while the bond between the central carbon atom and the nitrogen atom of imine group is a double bond. So, we can consider this also as a difference between amino acid and imino acid.
Summary – Amino Acid vs Imino Acid
Most people confuse the two terms amino acid and imino acid thinking they are the same. However, there is a distinct difference between amino acid and imino acid. The key difference between amino acid and imino acid is that an amino acid contains an amino group and a carboxylic group together in the same molecule whereas an imino acid contains an imino group and a carboxylic group together.
Reference:
1. N.V. Bhagavan, Chung-Eun Ha, in Essentials of Medical Biochemistry (Second Edition), 2015
Image Courtesy:
1. “Molecular structures of the 21 proteinogenic amino acids” By Dan Cojocari – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Imine-(primary)-skeletal” By Hbf878 – Own work (CC0) via Commons Wikimedia