Nonessential Amino Acids – Definition, Functions, Structure, Source

Nonessential amino acids play a crucial role in human health and biological processes, despite their misleading name. The term “nonessential” does not imply that these amino acids are unimportant; rather, it means that the body can synthesize them internally and does not require them from dietary sources. These amino acids support various functions including protein synthesis, cell growth, and tissue repair. They also contribute to the production of hormones, neurotransmitters, and other vital molecules. Understanding the role and importance of nonessential amino acids provides insight into their impact on overall health and well-being.

What are Nonessential Amino Acids?

Nonessential amino acids are those amino acids that the human body can synthesize on its own and do not need to be obtained directly through the diet. These amino acids are crucial for various bodily functions, including protein synthesis, enzyme production, and metabolism, but because the body can produce them, they are labeled as “nonessential” in the context of dietary requirements.

1. Alanine
2. Arginine (conditionally essential)
3. Asparagine
4. Aspartic acid
5. Cysteine (conditionally essential)
6. Glutamic acid
7. Glutamine (conditionally essential)
8. Glycine
9. Proline
10. Serine
11. Tyrosine (conditionally essential)

11 Nonessential Amino Acids

1. Alanine
   • Function: Alanine is crucial for transferring nitrogen from peripheral tissues to the liver and is involved in glucose metabolism, which helps regulate blood sugar levels.
   • Synthesis: It is produced from pyruvate and branched-chain amino acids.
2. Arginine (Conditionally Essential)
   • Function: Arginine supports immune function, hormone secretion, and ammonia detoxification. It is also a precursor to nitric oxide, essential for vascular health.
   • Synthesis: Made from citrulline, arginine becomes essential during times of rapid growth, disease, or trauma.
3. Asparagine
   • Function: Asparagine is important for amino acid transformation and metabolic control in nerve and brain tissue.
   • Synthesis: It is formed from aspartic acid and ammonia.
4. Aspartic Acid
   • Function: Aspartic acid participates in the urea cycle and DNA metabolism and aids neurotransmitter synthesis and nervous system functioning.
   • Synthesis: Derived from oxaloacetate, a component of the citric acid cycle.
5. Cysteine (Conditionally Essential)
   • Function: Cysteine is critical for protein synthesis, detoxification, and is a key component of glutathione, a major antioxidant.
   • Synthesis: Synthesized from methionine and serine, it requires sufficient dietary methionine.
6. Glutamic Acid
   • Function: As a neurotransmitter, glutamic acid is essential for brain signaling and also aids in synthesizing other amino acids.
   • Synthesis: Formed by adding ammonia to glutamate, facilitating nitrogen transport.
7. Glutamine (Conditionally Essential)
   • Function: Glutamine supports immune system function, intestinal health, and aids in ammonia excretion. It serves as a major fuel source for intestinal and immune cells.
   • Synthesis: Produced from glutamate and ammonia, its demand increases during physical stress or illness.
8. Glycine
   • Function: Glycine is involved in constructing DNA and RNA and is a significant component of collagen, affecting the central nervous and digestive systems.
   • Synthesis: It can be synthesized from serine and threonine, which are derived from the diet.
9. Proline
   • Function: Proline plays a role in protein synthesis and is a major component of collagen, supporting skin, ligaments, and joints.
   • Synthesis: Formed from glutamate, it is crucial for maintaining collagen structure.
10. Serine
    • Function: Serine is involved in the synthesis of proteins, fatty acids, and genetic materials, and plays a role in cell proliferation.
    • Synthesis: Produced from glycine or threonine, it is integral to cell growth and function.
11. Tyrosine (Conditionally Essential)
    • Function: Tyrosine is a precursor to important neurotransmitters like dopamine, norepinephrine, and epinephrine, influencing mood, alertness, and the stress response.
    • Synthesis: Derived from phenylalanine, it becomes essential if phenylalanine levels are insufficient.

Functions of Nonessential Amino Acids

1. Protein Synthesis

All amino acids, including nonessential ones, are building blocks for proteins. Proteins perform countless functions in the body, such as catalyzing metabolic reactions, replicating DNA, responding to stimuli, and transporting molecules from one location to another.

2. Cell Growth and Repair

Nonessential amino acids contribute to cell growth and the repair of tissues throughout the body. They are particularly important in rapidly dividing cells, such as those in the skin, hair, and immune system.

3. Enzyme Production

Many nonessential amino acids are involved in the production and function of enzymes. Enzymes are proteins that speed up chemical reactions in the body, essential for digestion, energy production, and other metabolic processes.

4. Neurotransmitter Regulation

Certain nonessential amino acids serve as precursors or components of neurotransmitters, the chemical messengers that transmit signals across nerve cells. For example, aspartate and glutamate are important in brain function and cognitive ability.

5. Immune Function

Nonessential amino acids like glutamine are critical for the proper functioning of the immune system. Glutamine, for instance, provides energy to immune cells and is crucial during times of stress or illness when the demand for glutamine increases significantly.

6. Detoxification

Some nonessential amino acids play a role in detoxifying harmful substances in the liver. For instance, glycine aids in the synthesis of glutathione, a major antioxidant that protects cells from oxidative damage and helps detoxify chemicals.

7. Energy Production

Although not their primary role, some nonessential amino acids can be used to produce energy through various metabolic pathways, especially during prolonged exercise or periods of fasting.

8. Hormone Synthesis

Nonessential amino acids are involved in the synthesis of hormones that regulate metabolism, stress responses, and growth. For instance, tyrosine is a precursor for the synthesis of thyroid hormones and adrenal hormones like adrenaline.

Structure of Nonessential Amino Acids

Nonessential amino acids, which the body can synthesize on its own, each have unique molecular structures that are crucial for their specific functions. Here’s an overview of the molecular structures of nonessential amino acids:

1. Alanine – Alanine has a simple structure with a methyl group as its side chain, making it a nonpolar, aliphatic amino acid. Its structure can be denoted as CH3-CH(NH2)-COOH.
2. Arginine – Arginine is known for its complex structure that includes a three-carbon aliphatic straight chain, capped by a guanidino group. The structure is HN=C(NH2)-NH-(CH2)3-CH(NH2)-COOH.
3. Asparagine – Asparagine contains an amide group on its side chain that replaces the extra carboxyl group found in aspartic acid, making it less reactive. Its structure is H2N-CO-CH2-CH(NH2)-COOH.
4. Aspartic Acid – This amino acid features a carboxyl group attached to the beta carbon, rendering it acidic. Its structure is HOOC-CH2-CH(NH2)-COOH.
5. Cysteine – Cysteine contains a thiol (sulfhydryl) group, which is important for forming disulfide bonds in proteins. Its structure is HS-CH2-CH(NH2)-COOH.
6. Glutamic Acid – Similar to aspartic acid but with an extra methylene group, glutamic acid has the structure HOOC-(CH2)2-CH(NH2)-COOH.
7. Glutamine – Similar to asparagine, glutamine includes an amide group but differs by having an extra methylene in its side chain. The structure is H2N-CO-(CH2)2-CH(NH2)-COOH.
8. Glycine – The simplest of all amino acids, glycine consists of a hydrogen atom as its side chain. Its structure is H-CH2-CH(NH2)-COOH.
9. Proline – Unique among the amino acids, proline forms a cyclic structure where the side chain is bonded to both the nitrogen of the amino group and the alpha carbon. Its structure is -(CH2)3-CH-CO-NH- (with the NH forming a ring with the alpha carbon).
10. Serine – Serine includes a hydroxymethyl group as its side chain, contributing to its polarity. The structure is HO-CH2-CH(NH2)-COOH.
11. Tyrosine – Tyrosine is distinguished by its aromatic ring and hydroxyl group, making it a polar amino acid. Its structure is HO-Ph-CH2-CH(NH2)-COOH, where Ph represents a phenyl group.

Sources of Nonessential Amino Acids

1. Alanine

• Sources: Meat, poultry, fish, dairy products, and eggs. Alanine is also found in significant amounts in protein-rich plant foods like beans and nuts.

2. Arginine (Conditionally Essential)

• Sources: Beef, pork, poultry, fish, dairy products, nuts, seeds, and legumes such as soybeans and chickpeas. Whole grains like oats and wheat also contain arginine.

3. Asparagine

• Sources: Asparagus, which is notably rich in asparagine, potatoes, legumes, nuts, seeds, beef, eggs, seafood, and whole grains.

4. Aspartic Acid

• Sources: Animal sources such as beef and poultry, eggs, and dairy products. Plant sources include sprouting seeds, oat flakes, avocado, asparagus, and wild game.

5. Cysteine (Conditionally Essential)

• Sources: High-protein foods such as pork, poultry, eggs, dairy products, onions, garlic, brussels sprouts, and broccoli. Wheat germ and granola also contain cysteine.

6. Glutamic Acid

• Sources: Cheese, especially Parmesan, beef, chicken, milk, and eggs. Plant-based sources include tomatoes, mushrooms, broccoli, and peas.

7. Glutamine (Conditionally Essential)

• Sources: Beef, chicken, fish, eggs, milk, and dairy products. For vegetarians, beans, beets, and spinach are good sources.

8. Glycine

• Sources: Meat, fish, dairy products, and legumes. Glycine is also found in high concentrations in gelatin and collagen-rich foods.

9. Proline

• Sources: Egg whites, dairy products, beef, and chicken. Plant sources include soy protein, asparagus, and mushrooms.

10. Serine

• Sources: Soybeans, nuts, chickpeas, eggs, beef, and fish. Dairy products like cheese and milk also contain serine.

11. Tyrosine (Conditionally Essential)

• Sources: High in almonds, avocados, bananas, dairy products, beans, seeds, and meats like chicken and turkey.

Health Benefits of Non-Essential Amino Acids

1. Supports Immune Function

Non-essential amino acids like glutamine are vital for the proper function of the immune system. Glutamine, for instance, serves as a fuel source for white blood cells and other immune cells, helping to maintain their function and prevent infections.

2. Enhances Brain Health

Amino acids such as glutamic acid and aspartic acid are important for normal brain function. They serve as neurotransmitters and are involved in signaling pathways within the brain that enhance cognitive processes and emotional well-being.

3. Promotes Wound Healing and Tissue Repair

Arginine and glutamine play significant roles in healing and tissue repair. Arginine is essential for the production of nitric oxide, which improves blood flow and oxygen delivery to healing tissues. Glutamine, on the other hand, helps in cellular proliferation necessary for repairing damaged tissues.

4. Aids in Metabolism and Energy Production

Amino acids such as alanine and aspartic acid are involved in the metabolism of glucose and fatty acids, providing energy to cells throughout the body. This is particularly important during periods of intense physical activity or stress.

5. Maintains Skin, Hair, and Nail Health

Cysteine, a sulfur-containing amino acid, is crucial for the synthesis of keratin, a protein that is a major component of skin, hair, and nails. It helps in maintaining their strength, elasticity, and appearance.

6. Supports Detoxification Processes

Glycine plays a critical role in the body’s detoxification process. It helps in the creation of glutathione, a major detoxifying agent in the body, which protects cells from oxidative damage and helps remove harmful substances.

7. Regulates Mood and Stress

Tyrosine is a precursor to several important neurotransmitters, including dopamine, epinephrine, and norepinephrine. These chemicals are crucial for regulating mood, stress response, and mental alertness.

8. Contributes to Digestive Health

Glutamine is an essential fuel source for the cells lining the intestines and can help maintain the integrity of the gut barrier. This is vital for preventing the leak of harmful substances into the bloodstream and for the absorption of nutrients.

9. Supports Muscle Growth and Function

Amino acids like proline and arginine are important for muscle metabolism. They help in muscle repair, growth, and maintenance, which are crucial for athletes and those engaged in regular physical activities.

10. Improves Heart Health

Arginine is known for its ability to improve blood flow by dilating blood vessels. This can help lower blood pressure and improve cardiovascular health.

Effects of Nonessential Amino Acid Deficiency

Nonessential amino acids, while synthesized by the body, are still crucial to various physiological processes. A deficiency in these amino acids, although rare due to their endogenous production, can occur under certain conditions like malnutrition, illness, or metabolic disorders, leading to various health issues.

Common Effects of Deficiency

1. Reduced Muscle Mass and Weakness
   • Explanation: Amino acids are the building blocks of proteins, which are essential for muscle growth and maintenance. A deficiency can lead to muscle wasting and reduced strength.
2. Poor Immune Function
   • Explanation: Nonessential amino acids like glutamine and arginine play vital roles in maintaining immune health. A deficiency may impair the immune response, making the body more susceptible to infections.
3. Digestive Problems
   • Explanation: Amino acids like glutamine are critical for intestinal health. Glutamine is a primary energy source for intestinal cells; its deficiency can lead to issues such as poor nutrient absorption and gastrointestinal discomfort.
4. Slow Wound Healing
   • Explanation: Amino acids like arginine and glycine are important for healing wounds. Arginine enhances collagen production and glycine is a key component of collagen. A deficiency may result in slower wound healing and recovery from injuries.
5. Mood Disorders
   • Explanation: Tyrosine is a precursor to several important neurotransmitters, including dopamine, norepinephrine, and epinephrine. Deficiencies in tyrosine can lead to mood swings, depression, and a general decrease in mental well-being.
6. Fatigue
   • Explanation: Amino acids are involved in energy production. Deficiencies, especially in amino acids like glutamine, can result in a lack of energy and chronic fatigue.

Conditionally Essential Amino Acids

Conditionally essential amino acids occupy a unique position between essential and nonessential amino acids. Unlike essential amino acids, which the body cannot synthesize and must obtain from the diet, or nonessential amino acids, which the body can produce on its own, conditionally essential amino acids are typically synthesized by the human body. However, under certain circumstances such as illness, stress, or intensive physical activity, the body’s ability to produce these amino acids may not meet its needs. In such cases, these amino acids become “conditionally essential,” meaning they must be obtained through the diet.

Some of the common conditionally essential amino acids include arginine, cysteine, glutamine, tyrosine, glycine, ornithine, proline, and serine. Each plays critical roles in various physiological processes:

• Arginine helps in wound healing, helps the kidneys remove waste products, and supports immune and hormone function.
• Cysteine is vital for making the antioxidant glutathione, which is important for cellular protection against oxidative stress.
• Glutamine serves as fuel for immune cells and intestinal cells, supporting both immune function and intestinal health.
• Tyrosine is a precursor to neurotransmitters such as dopamine, norepinephrine, and epinephrine, which are crucial for brain function and mood regulation.
• Glycine supports the production of other chemicals in the body, helps in the creation of muscle tissue and the conversion of glucose into energy.
• Ornithine is involved in the urea cycle, which helps detoxify ammonia and generates arginine.
• Proline contributes to the production of collagen and cartilage, supporting joint and skin health.
• Serine is important in the metabolism of fats, fatty acids, and muscle growth, and it helps maintain a healthy immune system.

FAQs

Which of the 20 Amino Acids Are Non-Essential?

Out of the 20 standard amino acids, 11 are considered non-essential for humans.

Are There 11 Non-Essential Amino Acids?

Yes, humans have 11 non-essential amino acids that the body can synthesize on its own.

Are There 9 Non-Essential Amino Acids?

No, there are 11 non-essential amino acids, not 9. The body synthesizes these without dietary sources.

How to Remember Essential and Nonessential Amino Acids?

Use mnemonics: “Any Help In Learning These Little Molecules Proves Truly Valuable” for essential amino acids.

What Is the Best Way to Remember Essential Amino Acids?

Memorize the mnemonic: “PVT TIM HALL” (Phenylalanine, Valine, Threonine, Tryptophan, Isoleucine, Methionine, Histidine, Arginine, Leucine, Lysine).