Amino Acids

Known as the building block of proteins, amino acids are the molecules that contain both amine group and a carboxylic acid functional group with a side chain that differs among different amino acids. The basic constituent elements of an amino acid molecule are, carbon, oxygen, hydrogen, nitrogen and sometimes, sulfur. An amino acid is the basic unit of protein. To be more specific, a protein molecule is a linear chain of amino acids linked by peptide bonds.

In nature, hundreds of amino acids exist, but out of them, 20 amino acids are generally found in the human body as the components of proteins. All these 20 amino acids are critical for life. They are literally used by every cell of the body, to carry out a number of metabolic functions. Being the basic unit of proteins, amino acids are also the building blocks of the muscle tissues.

Types of Amino Acids

The first amino acid to be discovered was 'asparagine', which was isolated as a compound of asparagus in the year 1806 by French chemists Louis-Nicolas Vauquelin and Pierre Jean Robiquet. Afterwards, more amino acids were isolated and identified. Out of all the amino acids existing in nature, 20 amino acids are usually found as components of proteins and peptides in the human body. These 20 amino acids are classified into two main groups, essential and non-essential amino acids. Generally, 8 amino acids (phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, leucine and lysine) are classified as essential amino acids, for the reason that the human body cannot synthesize them. So, these eight amino acids have to be obtained from foods.

Additionally, arginine, cysteine, glycine, glutamine, histidine, proline, serine and tyrosine are considered as conditionally essential. This means that they are usually not required to be obtained from diet, but at times, they may not be produced in sufficient amounts. In such a case, these amino acids have to be obtained from diet or from supplements. The three other amino acids, known as tyrosine, histidine and arginine are essential for infants and young children, as their body cannot synthesize these nutrients in adequate amount. The distinction between essential and non-essential amino acids is not very clear. But usually, arginine, alanine, cysteine, glutamate, glutamine, aspartate, glycine, asparagine, serine and pyrrolysine are considered as non-essential amino acids. Out of all amino acids, leucine, valine and isoleucine are called branched chain amino acids, which are essential amino acids with non-linear aliphatic chain.

Functions of Amino Acids

As the basic unit of proteins, amino acids are vital for protein synthesis. They are used by the body for building and repairing muscles, ligaments, tendons, skin, hair and nails. They are required for cell growth, enzyme synthesis and also for supporting biochemical reactions and making antibodies and hemoglobin. Even some amino acids act as neurotransmitters, while others facilitate the functions of vitamins and minerals.

L-Arginine: Arginine amino acid is important for cardiovascular health. It assists liver detoxification along with maintaining a healthy immune system. It is required for the release of growth hormones and it may prove helpful in kidney disorders, as well as increasing sperm count and sperm motility in men.

L-Lysine: L- lysine or lysine is important for growth, as well as repair of muscles. Along with vitamin C, it plays an important role in collagen formation. Apart from this, this essential amino acid facilitates the absorption of calcium and the production of antibodies, enzymes and hormones. It can lower the level of triglyceride in the body, and may prove effective for treating cold sores and genital herpes.

L-Cysteine: Cysteine can fight against the highly reactive free radicals that cause cellular damage. It can assist the process of detoxification of the body systems, besides providing protection against copper toxicity.

L-Glycine: Glycine takes part in the production of glycogen, which is then stored in the liver. Glycogen is broken down to glucose whenever the body is in need of energy. Glycine also supports and strengthens the immune system.

Tyrosine: Tyrosine is basically required for the synthesis of catecholamines such as, dopamine and noradrenaline. It has been observed that individuals suffering from depression usually have low levels of tyrosine. This is the reason why, it is sometimes used in the treatment of depression.

L-Histidine: This amino acid is the precursor of histamine, which is the chemical released by the immune system during an allergic reaction. Histidine dilates the blood vessels and has been found to be beneficial for reducing the symptoms of rheumatoid arthritis.

Leucine: This branched amino acid helps to reduce the breakdown of muscle protein. It can facilitates the healing of broken bones and also the uptake of neurotransmitter precursors by the brain.

Glutamine: It is the most abundant amino acid found in the muscles and serves as an important source of energy. Glutamine also supports the immune functions of the body.

Isoleucine: It provides energy to the muscles, and prevents muscle wasting or breakdown. It plays an important role in the formation of hemoglobin as well.

Methionine: Methionine is the precursor of cysteine and creatine. In other words, our body can synthesize these two amino acids from methionine. In addition to these, methionine can help to remove toxic substances from the liver and facilitate liver regeneration. It may reduce the level of blood cholesterol as well.

Tryptophan: It is essential for growth and normal metabolism. Tryptophan is the precursor of the neurotransmitter, serotonin. Serotonin is known to calm the central nervous system. A low level of serotonin is often associated with conditions like, depression.

Foods with Amino Acids

Amino acids are basically found in foods of animal origin. Examples include, meat, eggs, poultry and dairy products. These are the complete sources of proteins, as they contain all the essential amino acids. Most of the plant food sources on the other hand, cannot provide all the essential amino acids that are required by the human body. Often, they do not contain one or more essential amino acids. This is the reason why, vegetarians are generally advised to include a variety of plant foods in their diet. The most important plant sources of proteins and amino acids are, beans, pulses, legumes, soy and soy products and whole grains.

Today, amino acids are largely used for preparing supplements. The amino acid supplements are particularly popular among athletes and body builders. They use these supplements for enhancing their performance, as well as to build up muscle mass. Apart from these, these are used as a part of medical treatment in conditions like, alcoholism, drug abuse, depression, stress, weight loss, eating disorders and chronic fatigue to name a few. They are also used in food technology and for the production of biodegradable plastics, animal feed, drugs and cosmetics.