Key Difference – Polar vs Nonpolar Amino Acids
Amino acids can be divided into two groups based on the polarity as polar amino acids and nonpolar amino acids. The key difference between polar and nonpolar amino acids is that polar amino acids have polarity whereas polarity is absent in nonpolar amino acids.
Amino acid are organic compounds. An amino acid is composed of an amine group (-NH2), carboxyl group (-COOH), the alkyl group as a side chain (-R) and a hydrogen atom (-H). Therefore, an amino acid is formed from four basic chemical elements; C, H, O and N. Amino acids are the building blocks of proteins. Amino acids can be categorized in different ways based on the structure, synthesis, and properties such as essential and nonessential, polar and nonpolar.
CONTENTS
1. Overview and Key Difference
2. What is Polar Amino Acids
3. What is Nonpolar Amino Acids
4. Side by Side Comparison – Polar vs Nonpolar Amino Acids in Tabular Form
5. Summary
What is Polar Amino Acids?
Polar amino acids are amino acids that have polarity. Polar amino acids can be found in three types as neutral amino acids, positively charged amino acids and negatively charged amino acids. Polar amino acids with no charge have no charge on the “R” group (side chain). These amino acids can be found participating in the hydrogen bond formation in protein molecules. Example, amino acids for this group, are serine, threonine, tyrosine, cysteine, glutamine, and asparagine.
Figure 01: Classification of Amino Acids
Polar amino acids with a positive charge contain more amino groups than carboxylic groups. Then the amino acid becomes more basic. These amino acids have the positive charge on the “R” group. The examples for this category include lysine, arginine and histidine.
Polar amino acids with a negative charge have more carboxyl groups compared to amine groups. Then the amino acid becomes more acidic. The negative charge of these amino acids can be found in the “R” group. Examples of this group include aspartic acid and glutamic acid.
What are Nonpolar Amino Acids?
Nonpolar amino acids are amino acids that have no polarity. That is because these amino acids have equal numbers of carboxylic acid groups and amine groups. This makes these nonpolar amino acids to have a neutral charge. They have no charge on the “R” group.
Nonpolar amino acids are hydrophobic. Examples of nonpolar amino acids include alanine, valine, leucine, isoleucine, phenylalanine, glycine, tryptophan, methionine and proline.
What is the Difference Between Polar and Nonpolar Amino Acids?
Polar vs Nonpolar Amino Acids |
|
| Polar amino acids are amino acids that have polarity. | Nonpolar amino acids are amino acids that have no polarity. |
| Polarity | |
| Polarity is present in polar amino acids. | Polarity is absent in nonpolar amino acids. |
| Hydrophobicity | |
| Polar amino acids are hydrophilic. | Nonpolar amino acids are hydrophobic. |
| Examples | |
| Examples of polar amino acids include serine, lysine and aspartic acid. | Alanine, valine, leucine, isoleucine, phenylalanine, glycine, tryptophan, methionine, proline. |
Summary – Polar vs Nonpolar Amino Acids
Amino acids are the building blocks of proteins. There are several different ways of grouping amino acids based on the structure and properties. Polar amino acids and nonpolar amino acids are categorized based on the polarity of the amino acid. The difference between polar and nonpolar amino acids is that polar amino acids have polarity whereas polarity is absent in nonpolar amino acids.
Reference:
1.“Polar Amino Acids.” Polar Amino Acids, Non Polar Amino Acids | [email protected]. Available here
2.“Amino Acid.” Wikipedia, Wikimedia Foundation, 16 Mar. 2018. Available here
3.Gorga, Frank R. “Non-Polar Amino Acids.” Non-Polar R Groups, 1999. Available here
Image Courtesy:
1.’Figure 03 04 02’By CNX OpenStax , (CC BY 4.0) via Commons Wikimedia
ALL amino acids are polar. They all have a positively charged nitrogen atom and a negatively charged oxygen atom. So they are all polar. When we talk of polar and nonpolar amino acids in biochemistry we are actually talking about their SIDE CHAINS. This does not contradict the fundamental fact that they are all polar, even if some of them have a polar side chain and others have a nonpolar side chain.