What Are the 20 Amino Acids in the Human Body?

Amino acids make up approximately 20% of the human body by weight and are fundamental to nearly every biological process. These organic compounds are the building blocks of proteins, which perform a vast array of critical functions from repairing tissue to regulating enzymes and hormones. Understanding these 20 foundational amino acids is key to appreciating how our bodies function at a molecular level.

Quick Summary

The human body requires 20 amino acids to build proteins, classified as essential (from diet), nonessential (body-produced), and conditional (needed during stress).

Key Points

• Amino Acid Function: All 20 amino acids serve as the building blocks for thousands of proteins essential for growth, repair, metabolism, and immune function.

• Dietary Necessity: The 9 essential amino acids must be consumed through the diet, as the human body cannot produce them on its own.

• Internal Production: The body can synthesize the 11 nonessential and conditionally essential amino acids, though dietary intake is still beneficial.

• Conditional Requirements: During specific times of stress, illness, or rapid growth, some nonessential amino acids become conditionally essential, requiring increased intake.

• Complete Proteins: Foods containing all nine essential amino acids are known as complete proteins, and include animal products like meat, eggs, and dairy, as well as plant-based options like soy and quinoa.

• Unique Side Chains: The distinctive 'R-group' or side chain of each amino acid determines its unique chemical properties and its role in protein structure and function.

The Building Blocks of Life

Amino acids are the fundamental units that link together to form proteins. While many different amino acids exist in nature, the human body uses a specific set of 20 alpha-amino acids to synthesize the thousands of unique proteins it requires for function. Each amino acid shares a common basic structure: a central carbon atom (the alpha-carbon), an amino group (-NH2), a carboxylic acid group (-COOH), and a hydrogen atom. What makes each amino acid distinct is its unique 'R-group' or side chain, which gives it specific properties like size, polarity, and electrical charge. These properties dictate how the amino acid will interact with others and influence the three-dimensional folding and final function of the protein it forms.

Classification of the 20 Amino Acids

Based on whether the human body can produce them, the 20 amino acids are categorized into three groups: essential, nonessential, and conditionally essential.

Essential Amino Acids (9 total) These cannot be synthesized by the body and must be obtained from the diet. A deficiency can impact growth and function.

• Histidine: Important for immune function and nerve protection.
• Isoleucine: Crucial for muscle metabolism and hemoglobin formation.
• Leucine: A key trigger for muscle protein synthesis and tissue repair.
• Lysine: Essential for hormone and enzyme production, and calcium absorption.
• Methionine: Plays a role in tissue growth and metabolism.
• Phenylalanine: A precursor for neurotransmitters like dopamine and epinephrine.
• Threonine: Important for collagen and elastin production.
• Tryptophan: A precursor for the mood-regulating neurotransmitter serotonin.
• Valine: Involved in muscle growth and energy production.

Nonessential Amino Acids (6 total) These can be produced by the human body and do not typically need to be acquired from food.

• Alanine: Involved in glucose metabolism and detoxification.
• Asparagine: Assists in nitrogen transport and nucleic acid synthesis.
• Aspartic Acid: Key to metabolic processes and synthesis of other amino acids.
• Glutamic Acid: Functions as a key neurotransmitter in the brain.
• Glycine: The simplest amino acid, crucial for cell growth and wound healing.
• Serine: Supports muscle growth and immune system function.

Conditionally Essential Amino Acids (5 total) Normally nonessential, these can become essential during times of illness, stress, or rapid growth when the body's synthesis cannot meet demands.

• Arginine: Important for protein synthesis and immune function, especially during recovery.
• Cysteine: Acts as an antioxidant and is important for collagen synthesis.
• Glutamine: Critical for brain function, immune health, and cellular growth.
• Proline: Vital for collagen formation and tissue repair.
• Tyrosine: A precursor for thyroid hormones and melanin.

Roles and Importance in Human Health

Beyond their role in protein synthesis, amino acids are involved in a multitude of functions essential for maintaining health. They can act as a source of energy, produce hormones and enzymes, and support the immune system. A balanced intake of all amino acids, particularly the essential ones, is crucial. High-quality protein sources like meat, eggs, and dairy contain all nine essential amino acids, making them 'complete proteins'. Plant-based diets, while potentially lower in some amino acids, can provide all necessary components when a variety of protein sources are consumed.

Comparison of Essential vs. Nonessential Amino Acids

Feature	Essential Amino Acids	Nonessential Amino Acids
Source	Must be obtained through diet.	Produced by the body, not strictly needed from food.
Number	9	6 (with 5 others conditionally essential)
Production	Body cannot synthesize, or not in sufficient quantities.	Body can synthesize from other amino acids or precursors.
Importance	Crucial for normal bodily functions; deficiency can cause issues.	Also critical for bodily functions but less reliant on diet.
Example	Leucine, Lysine, Tryptophan.	Alanine, Glycine, Serine.

Conclusion: Amino Acids and Optimal Health

All 20 amino acids play a vital, collective role in the human body, serving as the raw materials for a vast network of proteins. These proteins, in turn, are the operational machinery that powers our growth, repair, metabolism, and immune defenses. Whether they are essential, nonessential, or conditionally essential, each amino acid contributes to our overall health and physiological balance. A balanced, protein-rich diet is the most effective way to ensure the body has the necessary building blocks to thrive. Maintaining this nutritional balance is a cornerstone of long-term wellness.

For more information on the specific roles of amino acids and their importance in nutrition, consult the MedlinePlus Medical Encyclopedia.

Frequently Asked Questions

What is the primary function of amino acids?

The primary function of amino acids is to act as the building blocks for proteins. The body uses proteins, which are long chains of amino acids, for countless functions including building muscle, repairing tissue, creating hormones, and functioning as enzymes.

What are essential amino acids?

Essential amino acids are the nine amino acids that the human body cannot produce. They must be obtained from dietary sources to support the body's growth and proper functioning.

What are nonessential amino acids?

Nonessential amino acids are the amino acids that the body is capable of producing on its own. While not strictly required from the diet, they are still vital for various bodily processes.

What is a conditionally essential amino acid?

A conditionally essential amino acid is one that is typically nonessential but becomes essential during specific circumstances, such as illness, stress, or periods of rapid growth when the body cannot produce enough to meet its demands.

Are all proteins made from the same 20 amino acids?

Yes, while many different types of amino acids exist in nature, the proteins in the human body are made exclusively from a standard set of 20 alpha-amino acids. The sequence and number of these amino acids determine the unique structure and function of each protein.

Do I need to take amino acid supplements?

Most healthy individuals can obtain all the necessary amino acids by eating a balanced and varied diet. Supplements are generally not required unless recommended by a healthcare provider for specific health conditions or needs.

What happens if I have an amino acid deficiency?

A deficiency in essential amino acids can lead to negative health effects, including impaired growth and other disorders, especially if caused by severe malnutrition. Maintaining a balanced diet is key to avoiding deficiencies.

Can vegans get all 20 amino acids from their diet?

Yes, a vegan diet can provide all the necessary amino acids. While some plant-based foods are 'incomplete' proteins, eating a variety of different plant protein sources throughout the day, like legumes, seeds, and grains, can ensure a complete intake of all essential amino acids.