Amino Acid Library

Explore protein-building amino acids, metabolic intermediates, unusual natural amino acids and important derivatives.

Interactive biochemistry reference

Discover the building blocks of life

Learn what each compound does, where it comes from, its discovery story and what makes it special. Search, filter and open any entry for more detail.

reference entries

20Standard protein amino acids

2Additional genetically encoded

9Essential in adult human diets

ManyNon-proteinogenic varieties

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Understanding this library

The 20 standard amino acids are routinely used to build proteins. Selenocysteine and pyrrolysine are two additional genetically encoded amino acids used in certain organisms. Beyond these are many hundreds of naturally occurring non-proteinogenic amino acids, stereoisomers, modified residues, amino sulfonic acids and synthetic analogues. There is no universally agreed finite list of “all amino acids,” so this library provides the complete canonical set plus a substantial, curated selection of biologically important examples—not an exhaustive inventory of every known chemical compound. Historical discovery dates can vary depending on whether first synthesis, isolation, naming or structural characterization is counted. Sources listed below document key scientific and historical claims; some less-studied discovery histories are approximate. Dietary essentiality refers to human nutrition, and is context-dependent for some compounds. This is an educational reference, not medical or supplement advice.

The science behind the library

Meet the tiny molecules doing extraordinary things.

Every muscle movement, enzyme reaction and newly built protein depends on chemistry happening at a microscopic scale. At the center of much of it are amino acids — remarkable molecules that help living organisms build, maintain and regulate complex biological systems.

This guide turns amino acid biochemistry into an approachable journey through nutrition, molecular structure, human biology, food sources and scientific discovery.

Biochemistry Nutrition Discovery

Molecular anatomy α-Amino acid

Amino group

Carboxyl group

Variable side chain

Alpha carbon

Simplified neutral-form diagram. In water at physiological pH, amino acid groups are commonly ionized.

Explore with purpose

A biochemistry library that invites curiosity.

No endless scrolling through disconnected definitions. Discover amino acids through a searchable, organized reference built to make complex science easier to explore.

Search the science

Look up amino acids by name, abbreviation, biological function, food source or discovery details. Narrow the results with category filters and sorting.

Fast reference

Go beyond the basics

Explore the 20 standard protein-building amino acids, two additional genetically encoded amino acids and a curated collection of non-standard compounds and derivatives.

57 entries

Uncover the backstory

Learn what compounds do inside living systems, where they occur naturally and how scientists identified, isolated or characterized them.

More than definitions

Back to the foundations

What exactly are amino acids?

Amino acids are organic compounds containing amino and carboxyl functional groups. The familiar protein-building alpha-amino acids have both groups associated with the same central carbon atom.

When cells produce proteins, ribosomes connect amino acids into chains through peptide bonds. These chains then fold into structures that carry out biological work, including catalyzing reactions, transporting substances and providing structural support.

But not every amino acid becomes part of a protein. Many occur as free metabolites, specialized natural products or modified molecular building blocks.

Think of it like a molecular alphabet: a relatively small collection of building blocks can be combined into an enormous diversity of proteins, with their order and chemistry influencing the final structure and function.

From sequence to structure

How proteins begin

Met

—

Ala

—

Gly

—

Leu

A polypeptide chain

An illustrative four-residue sequence

Protein folding

Longer chains can form functional three-dimensional structures

Conceptual illustration — real proteins are typically much longer and folding depends on sequence and environment.

The classification guide

Not all amino acids are created equal.

In human nutrition, amino acids are commonly grouped according to whether the body can synthesize enough of them to meet its needs. This is different from classifying them by chemical structure or their role in protein synthesis.

Dietary requirement

Essential amino acids

Humans cannot synthesize these nine amino acids in sufficient amounts, so they must be supplied by the diet.

Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Threonine Tryptophan Valine

Produced by the body

Nonessential amino acids

Nonessential does not mean unimportant. It means the body can ordinarily synthesize these amino acids rather than relying entirely on dietary supply.

Alanine

Asparagine

Aspartic acid

Glutamic acid

Serine and glycine

Context matters

Conditionally essential

Some amino acids may need additional dietary supply during certain stages of life or periods of metabolic stress, when synthesis cannot meet demand.

Arginine

Important during growth and some stress states.

Glutamine

Demand can rise in severe metabolic stress.

Cysteine and tyrosine

Depend partly on the availability of metabolic precursors.

These nutrition categories can overlap by context. The library's 20 standard proteinogenic amino acids include nine that are indispensable in the human diet; selenocysteine and pyrrolysine belong to a separate genetic-encoding classification.

Inside your biology

Small molecules. Remarkable responsibilities.

Amino acids participate in much more than protein construction. Their chemistry connects nutrition to metabolism, cellular communication, tissue structure and countless enzyme-controlled reactions.

Muscles and tissue repair

Protein synthesis uses amino acids to build and renew proteins in muscle, skin and other tissues. Leucine also participates in nutrient-sensitive signaling pathways.

Brain and nerve signaling

Glutamate and glycine act as neurotransmitters. Tryptophan and tyrosine are precursors used to synthesize important signaling molecules.

Antioxidant defenses

Cysteine, glycine and glutamate contribute to glutathione synthesis. Selenocysteine occurs in enzymes involved in cellular redox regulation.

Energy and metabolism

Amino acids can contribute carbon skeletons to energy pathways and help move nitrogen between tissues during normal metabolism.

Collagen and structural strength

Glycine, proline and hydroxyproline are especially relevant to collagen structure, which contributes to connective tissue organization.

Molecular synthesis

Amino acids supply atoms and chemical groups for producing nucleotides, heme, creatine and many other biologically important compounds.

From food to molecules

Where do amino acids come from?

Dietary protein is digested into amino acids and small peptides that the body can absorb and use. Both animal and plant foods can contribute essential amino acids.

Animal sources

Fish, eggs, dairy, poultry and meat.

Plant sources

Soy, lentils, beans, nuts, seeds and grains.

A well-planned plant-based diet can provide all nine essential amino acids.

Everyday nutrition examples

An amino acid tour through the kitchen

These are examples of foods that provide protein and amino acids. Actual amounts depend on the food, serving size and preparation.

Eggs and dairy products

Contain all nine essential amino acids in their proteins and are commonly used as examples of complete dietary protein sources.

Soybeans, tofu and tempeh

Plant-based sources of all nine essential amino acids, with protein content varying by product.

Beans, lentils and chickpeas

Provide useful amounts of protein and lysine, alongside fiber and other nutrients.

Fish, poultry and meat

Rich dietary protein sources that generally supply the full range of essential amino acids.

Grains, nuts and seeds

Contribute amino acids in varied proportions and complement other protein sources within an overall diet.

A fascinating distinction

Are there really only 20 amino acids?

No. The number 20 refers to the canonical amino acids routinely used to construct proteins through the standard genetic code.

Selenocysteine and pyrrolysine are two additional genetically encoded amino acids used by particular organisms through specialized translation mechanisms.

Beyond proteinogenic amino acids, nature contains many other amino acids and related chemical compounds — including metabolic intermediates, modified residues and specialized products of plants and microorganisms.

Standard proteinogenic amino acids

The canonical protein-building set taught in introductory biochemistry.

Additional genetically encoded amino acids

Selenocysteine and pyrrolysine, incorporated by specialized translation systems.

A much larger chemical world

Hundreds of naturally occurring non-proteinogenic amino acids, plus many synthetic compounds and derivatives.

About this library: Its 57 entries are a curated reference, not a complete chemical registry. Some included substances are amino acid derivatives or related compounds rather than strict alpha-amino acids.

A journey through scientific history

From asparagus juice to the genetic code.

The story of amino acids stretches across more than two centuries of chemistry. Some were first identified in foods or biological tissues; others were understood only after breakthroughs in molecular biology.

Milestones worth knowing

1806

Asparagine opens a new chapter

Louis-Nicolas Vauquelin and Pierre Jean Robiquet isolated asparagine from asparagus, a landmark early discovery in amino acid chemistry.

1820

Glycine emerges from gelatin

Henri Braconnot isolated glycine from gelatin, helping reveal the chemical components of protein-rich material.

1850

Alanine and the Strecker synthesis

Adolph Strecker synthesized alanine, establishing a foundational reaction in the chemistry of amino acids.

1866

Glutamic acid from gluten

Karl Heinrich Ritthausen isolated glutamic acid from wheat gluten, a compound later recognized as important in metabolism and umami taste.

20th century

Proteins reveal their sequences

Advances in peptide chemistry, protein sequencing and molecular genetics clarified how amino acid order relates to proteins and genetic information.

1986–2002

Expanding the encoded repertoire

Selenocysteine was established as a genetically encoded amino acid in the 1980s; pyrrolysine was identified as another example in 2002.

Historical dates may refer to isolation, synthesis, structural identification or recognition of a biological role. Those are not always the same event.

Why discovery stories matter

Before scientists could read protein sequences or examine molecular structures with modern instruments, they worked with plant extracts, animal tissues and carefully designed chemical reactions.

Each discovery helped build a clearer picture of the chemistry of life.

Did you know?

Asparagine was named after asparagus. Glycine takes its name from a Greek word associated with sweetness. Theanine was discovered in tea, while glutamic acid became closely associated with the savory taste called umami.

Chemistry Language Food history

Nutrition terminology decoded

What makes BCAAs different?

Branched-chain amino acids (BCAAs) are a specific group of three essential amino acids: leucine, isoleucine and valine. Their side-chain structures distinguish them chemically from other amino acids.

They participate in normal protein metabolism, and leucine has a well-studied role in signaling pathways related to muscle protein synthesis.

However, the body needs all nine essential amino acids to synthesize proteins. BCAAs alone cannot substitute for a complete supply of indispensable amino acids.

Leucine

Leu

Isoleucine

Ile

Valine

Val

BCAAs are a subgroup of essential amino acids, not a separate replacement for the full set.

Your exploration guide

From a question to an answer in four steps.

Search a compound

Enter a name such as tryptophan, glycine or citrulline, or search by a related function or food.

Choose a category

Filter for standard, additional genetically encoded, other, essential or conditionally essential entries.

Open the details

Read about biological roles, food or natural sources, historical discovery and interesting properties.

Follow your curiosity

Compare different amino acids, learn their abbreviations and connect molecular chemistry to everyday biology.

Speak the language of biochemistry

A quick amino acid glossary

Beginner friendly

Proteinogenic amino acid

An amino acid incorporated into proteins by a ribosomal translation system.

Peptide bond

A covalent linkage connecting amino acid residues within peptides and proteins.

Side chain (R group)

The variable part of an alpha-amino acid that contributes to its chemical properties.

Essential amino acid

An amino acid that humans must obtain through dietary supply in sufficient amounts.

Non-proteinogenic amino acid

An amino acid that is not normally incorporated directly into proteins by ribosomal translation.

One-letter amino acid code

A standard single-character abbreviation, such as G for glycine or W for tryptophan.

Questions, answered

Amino acid FAQs: curiosity welcome.

From essential amino acids and protein-rich foods to the difference between amino acids and proteins, here are clear answers to common questions.

What are amino acids?

Amino acids are organic compounds containing amino and carboxyl groups. Certain amino acids are joined by peptide bonds to form proteins, while others serve functions in metabolism, chemical signaling or specialized biological pathways.

How many amino acids are there?

There are 20 standard proteinogenic amino acids and two additional genetically encoded amino acids, selenocysteine and pyrrolysine. Beyond these, hundreds of naturally occurring non-proteinogenic amino acids are known, along with numerous synthetic compounds and derivatives. The number depends on the chemical definition being used.

What are the nine essential amino acids?

Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. They are essential in human nutrition because the body cannot manufacture adequate quantities to meet normal requirements.

What is the difference between amino acids and proteins?

Amino acids are individual molecular building blocks. Proteins are chains of amino acid residues that fold into structures capable of carrying out biological functions. Proteins may consist of one or more polypeptide chains.

Do plant foods contain all essential amino acids?

Yes. Plant proteins contain essential amino acids, but their relative amounts vary. Foods such as soy provide all nine in useful proportions. A varied, adequately planned plant-based diet can also meet essential amino acid requirements without every individual food being a complete protein source.

What are BCAAs?

BCAAs are branched-chain amino acids: leucine, isoleucine and valine. All three are essential amino acids involved in protein and energy metabolism. They are a subset of essential amino acids, not a separate complete protein source.

Can the human body make amino acids?

The body can synthesize many amino acids through metabolic pathways. However, nine are classified as essential in the human diet. Some ordinarily synthesized amino acids may become conditionally essential when demand exceeds the body's production capacity.

Which amino acid was discovered first?

Asparagine is generally recognized as the first amino acid discovered, having been isolated from asparagus by Vauquelin and Robiquet in 1806. Historical accounts may distinguish first isolation, chemical synthesis and later structural characterization.

What is the smallest amino acid?

Glycine is the smallest standard proteinogenic amino acid. Its side chain is a hydrogen atom, making its alpha carbon achiral. Glycine is especially abundant in collagen and participates in several biosynthetic pathways.

Are taurine and creatine amino acids?

Taurine is an amino sulfonic acid rather than a conventional amino carboxylic acid. Creatine is a nitrogen-containing compound synthesized from amino acid precursors. Both are biologically related to amino acid metabolism, but neither is one of the 20 standard protein-building amino acids.

What are amino acid one-letter and three-letter codes?

Standard amino acids have shorthand codes used in protein sequences. For example, glycine is Gly or G, alanine is Ala or A, and tryptophan is Trp or W. Some non-standard amino acids have three-letter identifiers but no dedicated standard one-letter code.

Do I need amino acid supplements?

Many people can meet their amino acid needs through a varied diet supplying enough high-quality protein. Whether supplementation is appropriate depends on individual circumstances, dietary intake and medical considerations. Supplements are not a universal replacement for adequate nutrition.

Built for learning, grounded in biochemistry

This amino acid encyclopedia is intended as a readable educational reference for students, curious readers and anyone exploring nutrition or molecular biology. Scientific terminology and research continue to evolve, especially for less-common metabolites, modified residues and unusual amino acids.

Explore authoritative references

NCBI Bookshelf — Essential Amino Acids National Human Genome Research Institute — Amino Acid PubChem — Chemical Structures and Compound Information UniProt — Protein Sequence and Function Knowledgebase

Educational notice: The library does not diagnose health conditions, determine individual nutrient requirements or provide medical treatment advice. Discovery dates and biochemical classifications may vary across sources and contexts. The 57-entry collection is curated, not a complete list of every naturally occurring or synthetic amino acid.

Keep exploring

Every amino acid has a story.

Explore familiar protein-building amino acids and lesser-known molecules that help reveal how wonderfully complex living chemistry can be.

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