20 Amino Acids Explained: Structure, Types, Classification (2025)

This article explains what amino acids are and explores the different types of amino acids including the complete amino acids list of the 20 amino acids that are fundamental to life. Whether you are wondering how many amino acids are there or seeking to understand their amino acid structure, you’ll find clear, student-friendly explanations below.

Overview

They are organic compounds that serve as the building blocks of proteins. Every protein in our body is made up of long chains of amino acids, making them essential for growth, repair, and overall biological function. In simple terms, what are amino acids? They are molecules that contain both an amino group (–NH₂) and a carboxyl group (–COOH) attached to a central carbon. This fundamental concept is crucial to understanding how proteins are assembled.

General Properties of Amino Acids

• High Melting/Boiling Points: Due to their ionic nature, amino acids have high melting and boiling points.

• Crystalline Solids: They typically appear as white, crystalline solids.

• Taste and Solubility: Some amino acids are sweet, others tasteless or bitter. Most are water-soluble but insoluble in many organic solvents.

• Zwitterionic Form: In aqueous solutions, the amino acids structure commonly exists as a zwitterion—meaning the molecule carries both a positive and a negative charge.

Classification of Amino Acids

Essential and Non-Essential Amino Acids

The classification of amino acids is based on the body’s ability to synthesise them:

• Essential Amino Acids: These cannot be made by our bodies and must be obtained from our diet. Our essential amino acids list includes:

• Isoleucine, Histidine, Lysine, Leucine, Phenylalanine, Tryptophan, Methionine, Threonine, and Valine.

• Non-Essential Amino Acids: These are produced by the human body. Examples include:

• Alanine, Asparagine, Arginine, Aspartic acid, Glutamic acid, Cysteine, Glutamine, Proline, Glycine, Serine, and Tyrosine.

Read More: Difference Between Essential and Non-Essential Amino Acids

Amino Acids Structure

The amino acid structure is remarkably simple yet elegant. All types of amino acids share a common backbone:

H₂N–CH(R)–COOH

Here, the central (α) carbon is attached to:

• An amino group (–NH₂)

• A carboxyl group (–COOH)

• A hydrogen atom

• A unique side chain

20 Amino Acids List with Chemical Formulas

Below is the amino acids list of the 20 amino acids found in proteins, along with their chemical formulas:

IMPORTANT INFORMATION - Across all known life forms, there are 22 amino acids encoded by genes. The standard genetic code incorporates 20 of these, while two additional amino acids—selenocysteine and pyrrolysine—are introduced through specialised translation mechanisms.

Sources of Amino Acids

Amino acids are vital to many bodily functions, and they must be obtained from various food sources, especially the essential amino acids which the body cannot produce. Key sources include:

• Plant-Based Foods: Broccoli, beans, beetroots, pumpkin, cabbage, nuts, dry fruits, chia seeds, oats, peas, carrots, cucumber, green leafy vegetables, onions, soybeans, whole grains, peanuts, legumes, and lentils.

• Fruits: Apples, bananas, berries, figs, grapes, melons, oranges, papaya, pineapple, and pomegranates.

• Animal Products: Dairy products, eggs, seafood, chicken, meat, and pork.

Functions of Amino Acids

Amino acids perform a host of roles in the body:

Functions of Essential Amino Acids

• Phenylalanine: Crucial for nervous system health and memory enhancement.

• Valine: Promotes muscle growth and repair.

• Threonine: Supports immune system function.

• Tryptophan: Contributes to the production of vitamin B3 and serotonin—a hormone that regulates mood, sleep, and appetite.

• Isoleucine: Aids in haemoglobin formation and insulin synthesis.

• Methionine: Important for skin health and detoxification.

• Leucine: Stimulates protein synthesis and growth hormone release.

• Lysine: Essential for antibody, hormone, and enzyme production, as well as calcium absorption.

• Histidine: Vital for the production of red and white blood cells.

Functions of Non-Essential Amino Acids

• Alanine: Helps in detoxification and glucose production.

• Cysteine: Acts as an antioxidant and aids collagen synthesis.

• Glutamine: Supports brain function and nucleic acid synthesis.

• Glycine: Assists cell growth and wound healing.

• Glutamic Acid: Functions as a neurotransmitter and supports brain health.

• Arginine: Promotes protein synthesis and immune function.

• Tyrosine: Involved in thyroid hormone production and melanin synthesis.

• Serine: Supports muscle growth and immune protein synthesis.

• Asparagine: Facilitates nitrogen transport and DNA synthesis.

• Aspartic Acid: Plays a role in metabolism and the synthesis of other amino acids.

• Proline: Important for collagen formation and tissue repair.

Deficiency of Amino Acids

A deficiency in amino acids—whether from a lack of essential amino acids or imbalances in non-essential amino acids—can lead to various health issues. Symptoms may include:

• Edema

• Anaemia

• Insomnia

• Diarrhoea

• Depression

• Hypoglycaemia

• Loss of appetite

• Liver fat accumulation

• Skin and hair problems

• Headache, weakness, irritability, and fatigue

Interesting Facts & Real-World Applications

Here are some unique insights that set this guide apart:

• Sports Nutrition: Many athletes focus on a balanced intake of essential and non-essential amino acids to aid muscle repair and enhance performance.

• Medical Research: Recent studies are exploring how specific amino acid structure modifications can lead to innovative therapies for metabolic disorders.

• Daily Life: Beyond their role in proteins, amino acids are also used in cosmetics and skincare formulations due to their role in collagen production and skin elasticity.

Further Links:

• Deficiency Diseases

• Life Processes

• Types of Protein and its Function

• Protein Denaturation