About

Amino acids are the fundamental monomers that polymerize to form proteins, the workhorses of biological systems. The chemical properties of the side chain (R-group) dictate the protein's tertiary structure and function. Understanding these properties - polarity, charge, and steric hindrance - is a prerequisite for biochemistry and molecular biology.

This tool visualizes the 20 canonical amino acids encoded by the standard genetic code. It provides critical data including molecular weight, pKa values (for titration curves), and hydropathy indices. The distinction between essential (dietary requirement) and non-essential amino acids is also highlighted.

Formulas

At physiological pH (pH ≈ 7.4), amino acids exist as zwitterions. The net charge (Z) depends on the pH relative to the pKa of the carboxyl (pK₁), amino (pK₂), and side chain (pK_R) groups.

pI = pK_a1 + pK_a22

This formula applies to amino acids without charged side chains. For those with charged side chains, the pI is the average of the two pKa values that bracket the neutral species.

Reference Data

Name	3-Letter	1-Letter	Side Chain	Polarity	Mass (Da)
Alanine	Ala	A	Aliphatic	Non-polar	89.1
Arginine	Arg	R	Basic	Polar (+)	174.2
Asparagine	Asn	N	Amide	Polar	132.1
Aspartic Acid	Asp	D	Acidic	Polar (-)	133.1
Cysteine	Cys	C	Sulfur-containing	Non-polar	121.2
Glutamic Acid	Glu	E	Acidic	Polar (-)	147.1
Glycine	Gly	G	Aliphatic	Non-polar	75.1
Histidine	His	H	Basic (Aromatic)	Polar (+)	155.2
Lysine	Lys	K	Basic	Polar (+)	146.2
Tryptophan	Trp	W	Aromatic	Non-polar	204.2

Frequently Asked Questions

The polarity is determined by the R-group (side chain). If the side chain contains electronegative atoms (Oxygen, Nitrogen, Sulfur) capable of hydrogen bonding, it is generally polar. Hydrocarbon chains (alkyl groups) or aromatic rings (mostly) are non-polar and hydrophobic.

Proline is the only standard amino acid where the side chain connects back to the backbone nitrogen, forming a cyclic secondary amine. This rigid structure creates "kinks" in polypeptide chains and disrupts alpha-helices.

Essential amino acids cannot be synthesized by the human body de novo and must be obtained through diet. Non-essential amino acids can be synthesized by the body from other metabolic intermediates.

The isoelectric point is the pH at which the amino acid carries no net electrical charge. It is critical for techniques like isoelectric focusing and ion-exchange chromatography.