Amino Acids: Structures, Abbreviations, and Properties

Comprehensive vocabulary flashcards covering the 20 standard amino acids, their abbreviations, chemical structures, side-chain classifications, and biochemical properties.

Leucine (Leu, L)

An essential amino acid characterized by a nonpolar, hydrophobic isobutyl side chain ($-\text{CH}_2-\text{CH}(\text{CH}_3)_2$).

Glycine (Gly, G)

The simplest nonpolar amino acid, possessing a single hydrogen atom ($-\text{H}$) as its side chain.

Phenylalanine (Phe, F)

An essential, nonpolar amino acid containing a hydrophobic benzyl side chain ($-\text{CH}_2-\text{C}_6\text{H}_5$) formed by a phenyl ring attached to a methylene carbon.

Alanine (Ala, A)

A nonpolar amino acid featuring a single methyl group ($-\text{CH}_3$) as its side chain.

Valine (Val, V)

An essential branched-chain amino acid containing a nonpolar, hydrophobic isopropyl side chain ($-\text{CH}(\text{CH}_3)_2$).

Proline (Pro, P)

A nonpolar amino acid with an aliphatic three-carbon side chain that loops to form a covalent cyclic bond with both the $\alpha$-carbon and the backbone amino nitrogen atom.

Isoleucine (Ile, I)

An essential branched-chain amino acid possessing a nonpolar, hydrophobic sec-butyl side chain ($-\text{CH}(\text{CH}_3)\text{CH}_2\text{CH}_3$).

Methionine (Met, M)

An essential, nonpolar amino acid containing a hydrophobic sulfur-ether (thioether) side chain ($-\text{CH}_2\text{CH}_2-\text{S}-\text{CH}_3$).

Tryptophan (Trp, W)

An essential, nonpolar amino acid containing a bulky aromatic indole ring connected to a methylene bridge ($-\text{CH}_2$).

Cysteine (Cys, C)

A sulfur-containing amino acid with a reactive sulfhydryl (thiol) side chain ($-\text{CH}_2\text{SH}$).

Asparagine (Asn, N)

An uncharged polar amino acid bearing an aliphatic carboxamide side chain ($-\text{CH}_2\text{CONH}_2$).

Glutamine (Gln, Q)

An uncharged polar amino acid featuring a carboxamide functional group linked by two methylene carbons ($-\text{CH}_2\text{CH}_2\text{CONH}_2$).

Serine (Ser, S)

An uncharged polar amino acid with a primary hydroxyl (hydroxymethyl) side chain ($-\text{CH}_2\text{OH}$).

Threonine (Thr, T)

An essential, uncharged polar amino acid possessing a secondary alcohol group on its side chain ($-\text{CH}(\text{OH})\text{CH}_3$).

Tyrosine (Tyr, Y)

An uncharged polar amino acid with a phenol group attached to a methylene carbon ($-\text{CH}_2-\text{C}_6\text{H}_4-\text{OH}$).

Aspartic acid (Asp, D)

An acidic amino acid with a negatively charged carboxylate side chain ($-\text{CH}_2\text{COO}^-$) at physiological pH.

Glutamic acid (Glu, E)

An acidic amino acid bearing two methylene carbons and a terminal carboxylate group ($-\text{CH}_2\text{CH}_2\text{COO}^-$) that carries a negative charge at physiological pH.

Lysine (Lys, K)

An essential, basic amino acid characterized by a four-carbon aliphatic chain terminating in a positively charged amino group ($-\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{NH}_3^+$).

Arginine (Arg, R)

A basic amino acid terminating in a guanidinium group whose positive charge is stabilized by resonance, rendering it strongly basic.

Histidine (His, H)

An essential basic amino acid with an imidazole ring whose nitrogens have a relatively weak affinity for an $H^+$ and are only partly positively charged at neutral pH.

Guanidinium Group

The terminal functional group of arginine's side chain ($-\text{NH}-\text{C}(=\text{NH}_2^+)\text{NH}_2$), which is highly basic because its positive charge is stabilized by resonance.

Imidazole Ring Nitrogens (Histidine)

The ring nitrogen atoms of histidine that exhibit a relatively weak affinity for protons ($H^+$), causing the side chain to be only partly positive at neutral pH.

Essential Amino Acids

Amino acids designated with a star (including leucine, phenylalanine, valine, isoleucine, methionine, tryptophan, threonine, lysine, and histidine) that cannot be synthesized de novo by the organism and must be supplied in the diet.