Amino Acid Chart: A Comprehensive Overview (2025)

Amino acid structure

Amino acids are the basic units of proteins. There are more than 300 kinds of amino acids in nature, but only 20 kinds of amino acids are involved in protein synthesis. An amino acid consists of a central carbon atom (also called an alpha-carbon atom) connected to four different groups. These groups include:

Amino group (-NH2): This is an alkaline group with two hydrogen atoms and one nitrogen atom, giving amino acids certain alkaline properties.

Carboxyl group (-COOH): This is an acidic group containing one carbon atom, two oxygen atoms, and one hydrogen atom, giving amino acids their acidic properties.

Side chain (R group): The specific properties of each amino acid are mainly determined by its unique side chain (or side group), which is a hydrocarbon chain or ring structure containing different elements and functional groups. Differences in the side chain determine the difference between 20 common amino acids and affect their function and interaction in living organisms. According to the properties of R groups, amino acids can be divided into different categories such as non-polar amino acids, polar amino acids, acidic amino acids and basic amino acids.

The structure of most amino acids is asymmetrical, so there are left and right, left called L-type amino acids, right called D-type amino acids. Most amino acids are left-handed (eg levodopa), with the exception of glycine. The R base of glycine is H, and the two H's are the same, so there is no left or right spin.

Amino acid table

Amino acid chart

The amino acid chart visually presents the 20 standard amino acids, listing their full names, three-letter codes, single-letter abbreviations, and key characteristics such as the chemical properties of the side chain. This chart is an important tool for understanding amino acid polymorphism and function in the context of protein structure and function. The chart can also help identify patterns in amino acid sequences, which is important in fields such as bioinformatics and protein engineering. The chart can also classify amino acid side chains according to their properties:

Among them, the aromatic amino acids are: tryptophan, tyrosine, and phenylalanine; the imino acids are: proline; the sulfur-containing amino acids include: cysteine, methionine.

Download Amino Acid Chart as PDF

Non-polar (hydrophobic) amino acids

The side chains of these amino acids are mostly hydrocarbon structures that lack polarity and are therefore insoluble in water. They are usually found inside proteins and help them maintain their structure.

Glycine (Gly, G): Minimal and simple, which gives it flexible properties. Its side chain is just one hydrogen atom. Glycine is the constituent amino acid of endogenous antioxidant reduced glutathione, which is often supplemented by exogenous sources when the body is under severe stress, and is sometimes called semi-essential amino acid.

Alanine (Ala, A): has a methyl side chain and is a stable and inactive amino acid. It is mainly used in biochemical research, tissue culture, liver function determination, flavor enhancer, can increase the seasoning effect, and can also be used as a sour correction agent to improve the sour taste of organic acids.

Valine (Val, V): One of the branched chain amino acids commonly found in the interior of proteins to increase hydrophobic stability. Isobutyraldehyde can be synthesized as raw material.

Leucine (Leu, L): Similar to valine, it is also a branched chain amino acid that plays an important role in catabolism and anabolism.

Isoleucine (Ile, I): a branched chain amino acid that is involved in muscle metabolism and plays a key role in energy production. Isoleucine has two antipalm centers, so there are four stereoisomers and two diastereomers of L-isoleucine. The only naturally occurring isoleucine is L-isoleucine.

Methionine (Met, M): A sulfur-containing amino acid that is the start codon in biosynthesis.

Phenylalanine (Phe, F): contains an aromatic ring, is non-polar, but can be converted to form tyrosine.

Tryptophan (Trp, W): containing complex aromatic rings, Tryptophan is the largest amino acid and one of the least polar amino acids.

Proline (Pro, P): The only cyclic amino acid with carboxyl fluoride mode restriction that affects the conformation of protein structures. Proline comes in three forms: DL-proline, L-proline, D-proline, and what is commonly known as proline is L-proline.

Polar/uncharged amino acids

These amino acids have the ability to interact with water, but do not have an electrically charged side chain.

Serine (Ser, S): contains a hydroxyl side chain that can form hydrogen bonds and is a common participant in glycoprotein and phosphorylation reactions.

Threonine (Thr, T): Similar to serine, it also contains hydroxyl, usually located on the surface of proteins. Threonine is also the raw material for a class of highly effective and hypoallergenic antibiotics called monoamidins.

Asparagine (Asn, N): has an amide side chain and can be used as a glycosylation site.

Glutamine (Gln, Q): acts as a nitrogen source and is involved in nitrogen exchange in cells.

Acidic amino acids

Characterized by a negative charge, its side chain carries a negative charge at physiological pH.

Aspartic acid (Asp, D): Its carboxyl group is easily dissociated to provide a negative charge and plays an important role in enzyme activity and protein binding.

Glutamic acid (Glu, E): It plays an important role in foreignizing metabolism and also acts as an important signaling molecule in nerve conduction.

Basic amino acids

Characterized by a positive charge, its side chain carries a positive charge at physiological pH.

Lysine (Lys, K): acts as a fundamental element in protein structure and has a side chain amino group.

Arginine (Arg, R): Also on the surface of proteins, is particularly important when interacting with DNA.

Histidine (His, H): Its imidazole ring has a pKa close to the physiological pH, giving it unique electron transport capabilities.

Properties of amino acids

Amino acid pKa and pI values

Amino acids are facultative ions and have amphoteric dissociation properties, and the dissociation mode depends on the pH of the solution.

pKa1: Usually refers to the acid dissociation constant of the carboxyl group (-COOH). When pH < pKa1, carboxyl group exists in undissociated form. When pH > pKa1, most carboxyl groups dissociate to COO-.

pKa2: Usually refers to the acid dissociation constant of α-ammonium ion (-NH3+). When pH < pKa2, amino group exists as NH3+; When pH > pKa2, most of the amino groups dissociate to NH2.

pKa3: If the amino acid side chain contains acid-base dissociable groups (such as histidine, lysine, glutamic acid, etc.), the corresponding acid dissociation constant is pKa3.

pI: The isoelectric point (pI) of an amino acid is its state of zero net charge at a specific pH. Different amino acids have different isoelectric points, which affect their migration behavior in electric fields and are often used in electrophoretic analysis. pI can be obtained by calculating the pH of an amino acid with zero charge, usually pI = (pKa1 + pKa2)/2 for an uncharged amino acid.