Amino acid structure & classification

44 terms, alphabetically ordered

Acetylation

Addition of an acetyl group, often to a lysine amino group; can alter charge and protein interactions.

AlanineAla · A

A nonpolar amino acid with a methyl side chain.

Alpha carbonα-carbon

The central carbon next to the carboxyl carbon. In a standard amino acid it binds an amino group, hydrogen, and side chain.

Alpha helixα helix · alpha helices · α helices

A helical secondary structure stabilized by hydrogen bonds between a backbone carbonyl oxygen and an amide hydrogen four residues later.

Amino acidamino acids

A protein building block containing amino and carboxyl groups and a characteristic side chain.

Amino groupNH₃⁺ · NH₂

A nitrogen-containing functional group. A free amino acid’s amino group is typically protonated (NH₃⁺) near physiological pH; proline’s ring nitrogen is an exception to this formula.

ArginineArg · R

A basic amino acid with a guanidinium group, usually positively charged near physiological pH.

Aromatic

Containing a cyclic, conjugated ring system with delocalized electrons. Phenylalanine, tyrosine, and tryptophan have aromatic side chains.

AsparagineAsn · N

A polar, uncharged amino acid with an amide side chain.

AspartateAsp · aspartic acid · D

An acidic amino acid whose side chain is usually negatively charged near physiological pH.

Carboxyl groupCOO⁻ · COOH

An acidic functional group, COOH. In free amino acids it is usually deprotonated to COO⁻ near physiological pH.

Chiralitychiral

Having a structure that cannot be superimposed on its mirror image. Glycine is the only standard amino acid without a chiral alpha carbon.

CysteineCys · C

An amino acid with a thiol side chain. Two cysteines can form a disulfide bond.

Disulfide bond

A covalent sulfur–sulfur bond formed by oxidation of two cysteine thiol groups, which can stabilize protein structure.

Enzymeenzymes

A biological catalyst that speeds a reaction without being consumed. Most enzymes are proteins.

Essential amino acidessential amino acids

An amino acid that humans must obtain from food because it cannot be made in sufficient amounts.

GlutamateGlu · glutamic acid · E

An acidic amino acid whose side chain is usually negatively charged near physiological pH.

GlutamineGln · Q

A polar, uncharged amino acid with an amide side chain one carbon longer than asparagine’s.

GlycineGly · G

The smallest amino acid; its side chain is hydrogen. It is achiral and allows substantial backbone flexibility.

Glycosylation

Attachment of carbohydrate groups to a molecule, influencing protein folding, stability, trafficking, or recognition.

HistidineHis · H

A basic amino acid with an imidazole side chain. Mostly uncharged near physiological pH, it can accept or donate protons.

Hydrogen bondhydrogen bonds · hydrogen bonding

An attraction between a hydrogen bonded to an electronegative atom and another electronegative atom. Backbone hydrogen bonds stabilize protein secondary structure.

Hydrophobic

Interacting poorly with water. Nonpolar side chains often gather in a soluble protein’s interior.

IsoleucineIle · I

A nonpolar amino acid with a branched hydrocarbon side chain.

L configurationL amino acid · L amino acids

A stereochemical configuration assigned by comparison with L-glyceraldehyde. Most amino acids incorporated into proteins have this configuration; glycine is achiral. L does not specify the direction of optical rotation.

LeucineLeu · L

A nonpolar, hydrophobic amino acid with a branched hydrocarbon side chain.

LysineLys · K

A basic amino acid with a terminal amino group, usually positively charged near physiological pH.

MethionineMet · M

A nonpolar amino acid with sulfur in a thioether side chain. Unlike cysteine, it does not form disulfide bonds.

Methylation

Addition of a methyl group; modification of residues such as lysine can regulate protein interactions and gene expression.

Nonessential amino acidnonessential amino acids

An amino acid the body can normally synthesize. Some become conditionally essential during growth or illness.

pH

A measure of acidity, defined as the negative base-10 logarithm of hydrogen ion activity. Lower pH means greater acidity; pH influences amino acid charge.

PhenylalaninePhe · F

A nonpolar amino acid with an aromatic benzyl side chain.

Phosphorylation

Addition of a phosphate group, often to serine, threonine, or tyrosine in proteins; can regulate protein activity.

ProlinePro · P

An amino acid whose side chain loops back to the backbone nitrogen, restricting rotation and often creating bends.

R groupR groups · side chain · side chains

The variable side chain attached to an amino acid’s alpha carbon. It determines identity, polarity, charge, and chemical behavior.

SerineSer · S

A polar, uncharged amino acid with a hydroxyl-containing side chain.

ThreonineThr · T

A polar, uncharged amino acid with a hydroxyl group and a methyl group on its side chain.

TryptophanTrp · W

An amino acid with a bulky aromatic indole side chain; commonly grouped as nonpolar.

TyrosineTyr · Y

An aromatic amino acid with a phenolic hydroxyl group. Usually uncharged near physiological pH.

Ubiquitin

A small protein attached to other proteins to regulate their degradation, localization, or interactions.

Ubiquitination

Attachment of ubiquitin to a protein, commonly at a lysine residue. Certain ubiquitin chains signal proteasomal degradation.

UltravioletUV

Light with wavelengths shorter than visible light. Protein absorbance near 280 nm is mainly due to tryptophan and tyrosine.

ValineVal · V

A nonpolar, hydrophobic amino acid with a branched side chain.

Zwitterion

A molecule with both positive and negative formal charges and zero net charge. Amino acids with uncharged side chains commonly take this form near physiological pH.

No matching terms. Try a different name or abbreviation.