Amino acids

Amino acids are the building blocks of proteins necessary for bodybuilding and tissue repair. Because there are a number of amino acid groups, they can change proteins into a range of forms like simple, compound and complex types. Biologically, amino acids are the most essential part of every cell because they aid in constant repair and growth of each cell. Our cells need repair at regular intervals due to their wear and tear, some toxic and biological water produced inside them. Amino acids are a type of macromolecules necessary for many different functions of the body. The first few amino acids were discovered in the early 19th century. In 1806, French chemists Louis-Nicolas Vauquelin along with  Pierre Jean Robiquet have successfully isolated asparagine in asparagus. Cysteine was discovered in 1810 while Glycine and leucine were discovered 10 years later. During 1935, the last amino acid out of the 20, threonine was introduced by William Cumming Rose. However, these discoveries were used under different terminologies. First use of the term "amino acid" in the English language dates from 1898. This post provides you with the basic concepts of amino acids; structure, functions, properties, importance, and classification of amino acids. 

Structure of amino acids


An amino acid is an organic molecule containing a basic amino group (−NH2) and the acidic carboxyl group (−COOH) while each molecule of amino acid is made up of a central carbon (C) atom (the α-carbon), to which both the amino and a carboxyl group are attached. The remaining two bonds of the α-carbon atom are generally satisfied by a hydrogen (H) atom and the R group. The R group is a variant that determines the identity of the amino acid. For example; if the R group is a hydrogen atom, then the amino acid is glycine, suppose it’s a methyl ( CH3) group,then the amino acid is alanine. The chemical status of an amino acid is determined by the properties of the side chain.Because of this, valine and leucine are nonpolar and hydrophobic, while serine and glutamine exhibit hydrophilic side chains and the polar property. On the other hand, amino acids, such as lysine and arginine contains a positively charged side chains making them. Furthermore, Aspartate and glutamate are distinguished by their acidic nature because of the negatively charged side chains.

Ring structure and bonding

Right bonding allows a right sequence of amino acids in addition to the exact number of amino acids. This can determine the protein’s shape, size, and function. Amino acids form a structured series with the help of covalent bonds in between and these bonds known as a peptide bond. When 2 amino acids are covalently bonded by a peptide bond, the carboxyl group of one amino acid and the amino group that joins from the other end release a molecule of water, and the reaction is known as dehydration. Therefore, peptide bond formation is an example of a dehydration reaction. Furthermore, R-groups in some amino acids demonstrates some special properties that help them build the proteins in the right manner. With this regard, the R group in Proline links back to its own amino group, forming a ring structure and this is not the typical amino acid-like. Cysteine, on the other hand, contains a thiol (-SH) group and can form covalent bonds with other cysteines.


The amino acids are distinguished by the properties; colourless, nonvolatile, crystalline appearance. They decompose and melt at temperatures above 200 °C. The essential amino acids vary from different species depending upon their physiology. Though there are more than 300 amino acids in nature only 20 of them are standard and present in proteins as coded by our genes. Other non-standard amino acids are called the modified amino acids or non-protein amino acids which do not serve significance in our body.

Classifications of Amino Acids

Amino acids are classified both biologically and chemically. The biological basis of classification of amino acids is based on whether our body can synthesize it or not.

Classification based on the biological basis 

  1. Essential

  2. Conditionally essential

  3. Non-essential amino acids

Essential amino acids

These are the amino acids very much essential for the body, but they cannot be synthesized by our body on its own, therefore, they must be consumed regularly through the diet. Essential amino acids are derived from animal proteins such as meat, eggs and poultry. With the help of metabolism, our body cells help to break down the proteins into simple amino acids in order to utilize them. Essential amino acids are:

  1. Leucine

  2. Isoleucine

  3. Lysine

  4.  Threonine

  5. Methionine

  6.  Phenylalanine

  7.  Valine

  8.  Tryptophan

Conditionally essential amino acids

The conditionally essential amino acids are required only during a crisis. The demand for these amino acids go high during specific circumstances such as when the body suffers from a chronic disease. One of the best examples is the histidine, it is an amino acid fall under the semi-essential or conditionally essential amino acids category as our body needs them rarely.

Non-essential amino acids

There is no need to consume them through food as they are synthesized by our body itself. Some of them are, 

  1. Asparagine

  2. Alanine

  3. Arginine

  4. Aspartic acid

  5. Cysteine

  6.  Glutamic acid

  7. Glutamine

  8.  Proline

  9. Glycine

  10. Tyrosine

  11.  Serine

Classification based on the chemical composition

  1. Cysteine and Methionine (amino acids containing sulfur)

  2.  Asparagine, Serine, Threonine, and Glutamine (neutral amino acids)

  3. Glutamic acid and Aspartic acid (acidic); and Arginine and Lysine (basic)

  4.  Leucine, Isoleucine, Glycine, Valine, and Alanine (aliphatic amino acids)

  5.  Phenylalanine, Tryptophan, Tyrosine and Histidine (aromatic amino acids)

Classification  based on their chain structure

Based on the side-chain structure, amino acids are divided int0 4 categories as follows;

  1. Non-polar

  2. Polar

  3. Acidic and polar

  4. Basic and polar

Non-polar amino acids contain pure hydrocarbon alkyl or aromatic groups. Some of the Non-polar amino acids are Phenylalanine, Glycine, Valine, Leucine, Alanine, Isoleucine, Proline, Methionine and Tryptophan. Meanwhile, some of the amino acids have their side-chain such as  Tyrosine, Serine, Asparagine, Threonine, Glutamine, and Cysteine. If the side chain contains carboxylic acid they fall under acidic and polar. The amino acids in the acidic-polar classification are Aspartic Acid and Glutamic Acid. Basic and polar groups contain alkaline elements.  Some of the basic-polar amino acids are Lysine, Arginine, and Histidine.

 Classification  on the basis of Catabolism

1. Glucogenic amino acids ​​​serve as precursors for  glucineogenesis that forms glucose when needed by our body. For example, GAMD (Glycine, Alanine, methionine, Aspartic acid).

2. Ketogenic amino acids  breakdown thmselves to form ketone bodies. For example, Leucine and Lysine

Biological importance of amino acids

  1. Amino acids aid in the normal functioning our body organs at different levels.

  2. They act as mediators for managing issues with skeletal muscle function, atrophic conditions, sarcopenia, and cancer.

  3. Amino acids are essential during the cell cycle and protein synthesis.

  4. Some of them assist in cell signalling,  hormone production, homeostasis (cellular balance), gene expression and the phosphorylation of proteins.

  5. Artificial food products are used as amino acid supplements as they demonstrate antioxidant abilities.

  6. They act as precursors toproduce the low molecular weight nitrogenous compounds, which possess numerous biological importance.

  7. Many amino acids proven beneficial in the medical field because of their therapeutic properties.

  8. Patients with immune system problems  can use them as immune boosters.

  9. Many amino acid supplements are used in the treatment of protein deficiency.

  10. They are also used to treat  liver diseases, fatigue, trauma due to accident, sepsis and maple urine disease.

  11. Amino acids such as alanine-lysine-serine and d-Proline are used as antibiotics against Staphylococcus aureus, Staphylococcus epidermis and  Escherichia coli.

  12. Scientific studies have proved that the branched-chain essential amino acids can be effectively used as weight loss supplements as they can stimulate fat loss.

Dietary Sources and functions of most commonly used amino acids


Intake   per kg body weight

Primary sources  



38 mg


It is richly found in meat, eggs, soya,  and pumpkin seeds.

Lysine is the building block of proteins, which help to produce hormones, immune cells and enzymes.     


14 mg


Mainly seen in poultry, meat, fish, nuts and seeds, whole grains

Histidine aids in maintianing a normal pH(7 ), apart from  regulating haemoglobin


20 mg


Cottage cheese and wheat germ  

Useful to treat many nervous system disorders including spinal spasticity, multiple sclerosis and familial spastic paraparesis.


19 mg


Methionine is richly found in eggs, grains, nuts, and seeds.

Very important  in many cellular  functions and it is also used to prevent liver damage in acetaminophen 


24 mg


Found in cheese, peanuts, mushrooms, whole grains, and vegetables.

It is an α-amino acid used in the biosynthesis of proteins


19 mg


Plentiful in red meat, fish, eggs, cheese, lentils, nuts and seeds.

It is highly recommended to sports personalities and, bodybuilders and athletes because the primary function of Isoleucine is to boost energy levels and quick recovery from strenuous physical activity.


 42 mg


Dairy, soy, beans, and legumes are sources of

Promotes hormone secretions in the body. Leucine also assists in regulating the blood-sugar levels and promotes the growth of cells.  They are also essential to recover muscle and bone tissues.


 33 mg



Dairy products, meat, poultry, soya bean, fish, beans, and nuts.


Used to treat depression, pain and skin disorders.


 5 mg


Wheat germ, cottage cheese, chicken, and turkey.

The body uses tryptophan to help make niacin, melatonin, and serotonin. Serotonin is thought to produce healthy sleep and a stable mood

Synthesis of amino acids

Amino acids are produced both naturally and artificially. Our body can synthesize amino acids and the process is known as  biosynthesis. However, few of them can be synthesized commercially by using artificial enzymatic processes in the industrial setup. For example ; Aspartic acid is produced by adding  ammonia to fumarate.

Read More

  1. Biomolecules in our body

  2. Digestion as a life process

  3. Recommended dietary intake

  4. Biotechnology principles and processes


  1. Distinguish between essential and non-essential amino acids.

  2. Explain the biological importance of amino acids.

  3. Mention the recommended daily intake of any 2 amino acids.

  4. Amino acids are responsible for repair and growth of body, explain.





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