Amino acids commonly found in proteins

Amino acid Click to bring up 3-D representation (separate window)	3-letter and 1 letter abbreviation	Description of R group
alanine	ala A	non-polar
arginine	arg R	basic, hydrophobic
asparagine	asn N	amide version of below - polar
aspartic acid	asp D	acidic - polar when ionised, otherwise can form hydrogen bonds
cysteine	cys C	polar; contains -SH (thiol) group (can form disulphide bridges with other cysteine residues); also very reactive with metal ions
glutamine	gln Q	amide version of below - polar
glutamic acid	glu E	acidic- polar when ionised, otherwise can form hydrogen bonds
glycine	gly G	simplest amino acid, allows full rotation of polypeptide chain: polar
histidine	his H	basic
isoleucine	ile I	non-polar
leucine	leu L	non-polar
lysine	lys K	basic
methionine	met M	non-polar, contains S
phenylalanine	phe F	non-polar, hydrophobic, aromatic ring
proline	pro P	(not a true amino acid: imino group >NH, cyclical shape so less possibility of chain rotation) non-polar
serine	ser S	polar
threonine	thr T	polar
tryptophan	trp W	non-polar, aromatic ring: quite reactive
tyrosine	tyr Y	polar, aromatic ring
valine	val V	non-polar

Notes about side chains
n.b. Each amino acid has both amino and carboxylic acid groups but these are are "used up" to form covalent peptide bonds, so do not confuse these with amino and carboxylic acid groups mentioned below.
Exception : the first amino and last carboxylic acid groups in the sequence (at either end of the polypeptide chain).

Acidic side chains can ionise and become negatively charged. Generally due to -COOH (carboxylic acid) groups in the R groups.
Basic side chains can ionise and become positively charged. Generally due to R groups containing extra nitrogen-containing groups (not always -NH₂: amino)

Polar side chains attract other polar side chains, and allow hydrogen bonding with other polar side chains. Hydroxyl (-OH) groups make them attracted to water (hydrophilic), so they often face outwards from molecule.
Non-polar side chains attract other non-polar side chains, forming hydrophobic bonds. Presence of hydrogen and alkyl groups, and lack of -OH groups make them repelled by water (hydrophobic), so they may face to centre of molecule.

Aromatic rings make bulky side chains which may affect coiling of the polypeptide chain.

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Mnemonics to help you remember 1-letter codes

Amino acid explorer

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