What Are Amino Acids Used for in Humans? Learn About the 20 Amino Acids Humans Need to Survive

Background

Over 500 amino acids exist in nature, but the human body only uses 20 of them. These amino acids serve as the basic units of proteins, which help carry out chemical reactions in cells and play a role in most cellular processes. The arrangement of amino acids determines the structure of proteins and the stability of these protein structures.

Alanine

The body has the ability to produce this amino acid, but you can also find it in meat, seafood, legumes, nuts, beans, whole grains and brown rice. Alanine plays a critical role in the glucose-alanine cycle, which occurs between the liver and other tissues. Muscles produce alanine during periods of oxygen deprivation. This alanine travels to the liver, where the liver uses it to make glucose.

Arginine

Arginine is classified as a “conditionally essential” amino acid. This means that it may or may not be essential, depending on the health and developmental stage of a person. Premature infants cannot produce this amino acid, so it is essential to give them arginine from dietary or supplement sources. Sources of arginine include meat, dairy products, seafood, fowl, granola, nuts, oatmeal and seeds. Arginine helps wounds heal, aids in proper immune function, participates in the removal of ammonia, contributes to the release of hormones and plays a role in cell division.

Asparagine

Asparagine is a nonessential amino acid that plays a role in nervous system function and production of ammonia. Dietary sources of asparagines include asparagus, legumes, beef, dairy products, nuts, whole grains, fish, eggs, seeds and seafood.

Aspartic Acid

Aspartic acid is a nonessential amino acid that assists in the production of glucose and stimulates glutamate receptors. Dietary sources of this amino acid include avocado, molasses and oat flakes.

Cysteine

Cysteine is a nonessential amino acid with several functions in the human body. It acts as an antioxidant, which means it helps combat the effects of free radicals on the cells. This amino acid also plays a role in the stability of proteins. Dietary sources of cysteine include pork, poultry, eggs, dairy products, red bell peppers, onions, garlic, granola, wheat germ and broccoli.

Glutamic Acid

Glutamatic acid is necessary for proper cell function and serves as a building block for proteins. It also acts as a neurotransmitter and plays a role in memory and learning processes. Sources of this amino acid include meat, eggs, kombu, dairy products, fish and poultry.

Glutamine

Glutamine is also a conditionally essential amino acid. Those who have gastrointestinal disorders and those who perform strenuous exercise may need to supplement glutamine production with supplements or dietary sources of this amino acid. Dietary sources of glutamine include dairy products, meat, eggs, poultry, beets, cabbage, wheat, parsley and spinach. Glutamine aids in protein synthesis, helps produce ammonium, serves as a source of energy, donates carbon in the citric acid cycle and donates nitrogen for anabolic processes in the body.

Glycine

Glycine is another nonessential amino acid with multiple functions. It acts as a neurotransmitter in the spinal cord, retina and brain stem. It also aids in the synethesis of D-Aminolevulinic acid and donates the C2N unit to purines.

Histidine

Histidine is one of the 10 essential amino acids. It acts as a precursor to histamine and aids in the synthesis of carnosine. It also plays a role in the synthesis of urocanic acid and ammonia. If a person lacks histidine ammonia-lyase, it results in histidinemia, a rare metabolic disorder.

Isoleucine

Isoleucine is an essential amino acid, which means you need to ingest it. Dietary sources of this amino acid include chicken, lamb, turkey, fish, eggs, cheese and seaweed. The carbon skeleton of isoleucine can be used for the production of glucose or fed into the citric acid cycle to play a role in oxidation.

Leucine

Leucine, an essential amino acid, is used by the liver, fat tissue and muscle tissue. The fat and muscle tissue use leucine to form a subgroup of steroids known as sterols. This amino acid also stimulates the production of muscle protein and slows the breakdown of muscle tissue. Leucine also has a use as a food additive used to enhance flavors. Sources of this amino acid include peanuts, almonds, oats, soy protein, beans, rice, lentils and corn.

Lysine

Lysine is an essential amino acid that serves as a base. This substance aids in hydrogen bonding and as a general base in changing the speed of chemical reactions. Dietary sources of lysine include soybeans, catfish, beef, lentils, chicken, milk, split peas, chickpeas, kidney beans and eggs. This amino acid also aids in calcium absorption, the production of muscle protein, hormone production, recovery from trauma to body tissues and the production of antibodies and enzymes.

Methionine

The essential amino acid methionine acts as an intermediate in the production of taurine, cysteine, lecithin, carnitine and other substances. Sources of methionine include Brazil nuts, oats, soy protein, peanuts, sesame seeds, yellow corn, wheat germ, chickpeas, lentils, almonds and brown rice.

Phenylalanine

Essential amino acid phenylalanine serves as a precursor to substances like dopamine, epinephrine, norepinephrine and melatonin. It also has analgesic – pain relief – and antidepressant effects. Sources of this amino acid include cod, organ meat, cheese, chicken, seeds, milk, tofu, eggs and soy protein.

Proline

Proline, a nonessential amino acid, has applications in the biotechnology and pharmaceutical industries. It is often used to change the rate at which organic reactions occur. It also serves as a structural component of proteins.

Serine

The body produces serine, so it is not an essential amino acid. One of its most important uses is in metabolism, as it helps produce pyrimidines and purines. It also acts as a precursor to other substances and aids in the function of enzymes.

Threonine

Threonine is an essential amino acid and is one of only two common amino acids that contain an alcohol group. Dietary sources of this amino acid include fish, cottage cheese, lentils, poultry, sesame seeds and meat. This amino acid can appear on the surface of a protein or within the interior of a protein. The hydroxyl group in this amino acid helps it form hydrogen bonds with other substances.

Tryptophan

Tryptophan, known for its presence in turkey, is an essential amino acid. Additional sources of tryptophan include chocolate, dairy products, fish, seeds, peanuts, chickpeas, red meat and chicken. This amino acid serves as a precursor to niacin and serotonin.

Tyrosine

Tyrosine, a nonessential amino acid, receives phosphate groups in signal transduction processes and participates in the process of photosynthesis. Dietary sources of this amino acid include peanuts, avocados, dairy products, almonds, seeds, chicken, fish, soy products and turkey.

Valine

Valine is an essential amino acid found in poultry, fish, lentils, sesame seeds, cottage cheese and peanuts. It has hydrocarbon side chains, which make it a branched chain amino acid. This amino acid is a component of proteins.

References

University of Arizona: The Chemistry of Amino Acids

University of Maryland Medical Center: Phenylalanine