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On the forefront of discoveries that paved the path for research on amino acids were two French chemists Vauquelin and Robiquet who witnessed the formation of asparagine, an AA, in nature. In 1820, glycine became the first AA to be isolated from gelatin, a protein, through a chemical reaction with sulfuric acid. The term amino acid was coined by the French Chemist Broconnot and became commonly used in the English language in 1898.
By 1925, more than twenty AA had been discovered, and by the 1950s, the number had amounted to 200. This essay aims at giving a comprehensive definition of amino acids and drawing a clear line between essential and non-essential amino acid groups while explaining their roles in the human body.
Amino Acids in the Human Body
In modern science, amino acids are defined as organic compounds that include both amino and acid groups. Amino acids combine to create proteins, which are the building blocks of the human body. The human body needs twenty amino acids to function correctly (Starr, Taggart, & Evers, 2018). Nine of them are called essential because humans cannot produce them on their own and, hence, have to ensure their regular intake of food. The human body synthesizes nonessential amino acids in its cells. Most of the 11 nonessential AA (alanine, arginine, asparagine, aspartate, cysteine, glutamate, glutamine, glycine, proline, and serine) are derived from glucose (Ryadnov & Hudecz, 2016). The only exception is tyrosine, which the body synthesizes from phenylalanine – an essential AA.
Amino acids have remarkably different chemical properties and metabolic functions in the human body. Below is the list of all the essential amino acids with a short description of their role in maintaining good health:
- Lysine: building muscle and bone strength, facilitating recovery after an injury or surgery, and upholding hormonal balance as well as regulating antibodies and enzymes.
- Histidine: blood cell creation and tissue growth and repair. When metabolized into histamine by the human body, it strengthens the immune and reproductive systems.
- Threonine: skin and hair health, digestion, and mild depression prevention.
- Methionine: skin, hair, and nails strength.
- Valine: mental concentration, emotional stability, and muscle growth and coordination.
- Isoleucine: tissue repair, blood sugar moderation, and hormonal balance.
- Leucine: blood sugar regulation, tissue repair, and growth hormone production.
- Phenylalanine facilitates the proper use of other amino acids as well as enzymes and proteins.
- Tryptophan: serotonin (happiness hormone) and melatonin (sleep hormone) precursor (Ryadnov & Hudecz, 2016).
Amino Acid Deficiency and Dietary Recommendations
Animal products such as meat, poultry, eggs, and milk products are recognized as the best sources of essential amino acids for humans. This claim is often debated by the adherents of cruelty-free lifestyles – vegetarianism and veganism. Interestingly enough, the results of a recent study in males with different dietary habits showed that the concentration of methionine, tryptophan, and tyrosine in plasma was the highest in vegetarians and fish-eaters.
Meat eaters showed average results while vegans’ amino acid concentration was lower than adequate (Schmidt et al., 2016). Overall, there is no general consensus on whether a plant-based diet covers all human needs for essential amino acids.
Recommendations on dietary protein intake needed for maintaining good health also vary from guideline to guideline. As of now, a number of studies that examined age-related changes, weight loss, prolonged involuntary bed rest, and type 2 diabetes highlighted the advantages of heightened protein intake. On the contrary, some other recent research failed to reveal any additional value in protein-rich diets (Layman et al., 2015). Such contradictory findings might in part arise from varying definitions of protein adequacy which is based on the evaluation of the roles of amino acids.
The lack of conclusive findings does not mean that a person can neglect their diet. Amino acid deficiency can have a slew of unpleasant consequences. Shortage in AA caused by the lack of dietary protein results in persisting feelings of fatigue, dizziness, and sickness. Long-term effects of a reduction in protein consumption cause a decrease in muscle mass, brittle hair, skin irritation, indigestion including diarrhea, and difficulty recovering from injury, surgery, or infection.
The studies on amino acids have a long, rich history dating back to the early 19th century when the field of organic chemistry was pioneered by European scientists. As of now, modern science is familiar with more than 200 AA, 20 of which are important for health and wellness.
The human body is capable of synthesizing the majority of AA from glucose and phenylalanine. The remainder of the list constitutes the essential amino acid group – something that a person needs to consume with food on a regular basis. Amino acids are incredibly diverse in their roles and functions. They are responsible for the immune, reproductive, and digestive systems as well as hair and nail growth and mental health. It is essential to avoid AA deficiency by maintaining a healthy diet rich in protein.
Layman, D. K., Anthony, T. G., Rasmussen, B. B., Adams, S. H., Lynch, C. J., Brinkworth, G. D., & Davis, T. A. (2015). Defining meal requirements for protein to optimize metabolic roles of amino acids. The American Journal of Clinical Nutrition, 101(6), 1330S-1338S.
Ryadnov, M., & Hudecz, F. (2016). Amino acids, peptides and proteins. London, UK: Royal Society of Chemistry.
Schmidt, J. A., Rinaldi, S., Scalbert, A., Ferrari, P., Achaintre, D., Gunter, M. J.,… & Travis, R. C. (2016). Plasma concentrations and intakes of amino acids in male meat-eaters, fish-eaters, vegetarians and vegans: a cross-sectional analysis in the EPIC-Oxford cohort. European Journal of Clinical Nutrition, 70(3), 306.
Starr, C., Taggart, R., & Evers, C. (2018). Biology: The unity and diversity of life (15th ed.). Boston, MA: Cengage Learning.