What are Neutral Amino Acids?

Amino acids which do not have any charge on them are neutral amino acids.

How are Neutral Amino Acids different from Basic and Acidic Amino Acids?

Amino acids are composed of two groups namely an amino group and a carboxylic acid group. The number of amino and carboxylic acid groups decides whether the given amino acid is acidic, basic, or neutral. Neutral amino acids are the amino acids that possess an equal number of amino and carboxylic acid groups. The groups attached to the amino acid, apart from the carboxylic acid groups and amino acid groups, may be either polar or non-polar. The amino acid that is non-polar contains alkyl groups as side chains and the polar amino acids contain a functional group.

Biomolecules - Proteins     

Every organism that grows, reproduces and sustains their own life, are composed molecules and atoms that are non-living. These atoms are interlinked by a covalent bond to form a molecule. Proteins, nucleic acid, carbohydrates, and lipids are a few of the complex macromolecules that make up the living species. Specifically, carbohydrates and protein are the significant constituents of our food. The interaction between these kinds of essential biomolecules constitutes the molecular basis of the organisms. Certain other simple molecules including minerals and vitamins also play their part in the composition of the organisms. Every biomolecule is made mainly of hydrogen and carbon atoms along with phosphorus, nitrogen, oxygen, and sulfur.     

This particular biomolecule is available enormously in living organisms. The main source of proteins is cheese, pulses, milk, fish, meat, and peanut. This presents in all the body parts and is responsible for forming the basic structural and functional units of life.

Protein is an essential factor for the body’s maintenance and growth. Proteins are classified as globular and fibrous proteins based on the shape of the molecule. The alpha-amino acid biopolymers of subunits make up all the proteins, biologically. Enzymes are also an example of proteins which act as a catalyst in several biochemical reactions.      

Amino Acids     

Amino acids are composed of two functional groups namely carboxyl and amino groups and they are differentiated as$\text{α, β, γ, δ}$, and so on. These are represented in three-letter and even in a single letter code. For example, glycine is represented as gly and G and proline is represented as pro and P. Amino acids are high melting solids that do not exhibit any color and exist as crystalline solids. These are generally water-soluble in nature and exhibit their character as salts. The amino acid polymers are interlinked by the peptide linkage.

Different types of amino acids

Amino acids can be divided into three types, i.e.,

• Acidic
• Basic
• Neutral

If the number of carboxylic acid groups is greater than that of the amino groups, then the amino acid is called an acidic category of amino acids. Glutamic and aspartic acid are acidic amino acids.

If the number of amino acid groups is greater than that of the carboxylic acid groups, then the specific amino acid is termed a basic amino acid. Histidine and lysine are basic amino acids.

If the number of amino and carboxylic acid groups is the same, then the amino acid is called neutral amino acids. Asparagine and glutamine are neutral amino acids.

Amino acids can also be further categorized into,

• Non-essential
• Essential
• Conditional

There are certain amino acids that are capable of being synthesized in the human body which are referred to as non-essential amino acids. Some of the non-essential amino acids are aspartate, alanine, asparagine, cysteine, glycine, arginine, proline, tyrosine, and serine. Alanine helps in the removal of toxic substances, cystine helps in the formation of skin, asparagine helps to balance the state of emotions, glycine is necessary for the healing of wounds, and proline helps in intracellular signaling.

Certain other amino acids need to be taken through diet, as they cannot be produced in the body, which are termed essential amino acids. Histidine, phenylalanine leucine, valine, threonine, isoleucine, lysine, tryptophan, and methionine are some examples of essential amino acids. Lysine helps to maintain bone strength, histidine helps in the repair of tissues, valine helps in muscle coordination, isoleucine helps in the regulation of blood sugar levels, leucine helps in repairing muscles and bones, and tryptophan is used as an ingredient in sleeping pills.

Conditional amino acids are those amino acids that are not essential under normal conditions but are necessary during stress or illness. Some of the conditional amino acids are glycine, arginine, glutamine, proline, tyrosine, and cysteine.   

Neutral Amino Acids

Amino acids are compounds that possess an amino group and a carboxylic acid group. Apart from these groups, the amino acids also contain a side chain R, which can be aliphatic, aromatic, or a functional group. The side chain R differs for varying amino acids. The number of amino and carboxylic acid groups decides whether the amino acid is acidic, basic, or neutral. Equal numbers of carboxyl and amino groups are present in neutral amino acids. More number of carboxyl groups than the amino groups makes the amino acid acidic. More number of amino groups than carboxyl groups makes the amino acid basic.

In aqueous solutions, the carboxyl group of amino acids gets deprotonated and the amino group gets protonated. So, the carboxyl group gains a negative charge and the amino group gains a positive charge. This form is known as the zwitter ion. Zwitter ion possesses both positive, as well as negative charges. Amino acids are used as an energy source for the human body.

Types of Neutral Amino Acids

The neutral amino acids can be divided into two types:

Non-polar amino acids: These amino acids contain an equal number of carboxylic and amino groups along with an R group which can be aliphatic or aromatic. Due to the existence of R groups, these amino acids are hydrophobic in nature. The globular proteins will undergo folding to form a shape such that the hydrophobic groups will be in the interior of the protein. The examples of non-polar amino acids are isoleucine, valine, alanine, tryptophan, leucine, glycine, methionine, proline, and phenylalanine.

Polar uncharged amino acids: In this type of neutral amino acids, the side chains contain functional groups which possess atoms like nitrogen, sulfur, and oxygen. These atoms possess a lone pair of electrons that help in the hydrogen bonds’ formation with water or other molecules. The examples of polar uncharged amino acids are threonine, cysteine, tyrosine, glutamine, serine, and asparagine.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for Bachelors and Masters in Chemistry and Biochemistry.