The 20 Common AMINO ACIDS

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GENERAL

STRUCTURE at right

we’ll see them in Chapter 19, so worry about them then!

Common Name
and Abbreviations

“IUPAC” Name

Line Structure

Comments

alanine
ALA
A

2-amino propanoic acid

“aliphatic”
nonpolar

arginine
ARG
R

2-amino-
5-guanidino
pentanoic acid

the side chain guanidino group is positively charged at pH 7;
a “basic” amino acid
extremely hydrophilic

asparagine
ASN
N 

aspartic acid b-amide

the “half amide” of aspartic acid
polar, neutral
hydrophilic

aspartic acid
ASP
D

2-amino butanedioic acid

the b-carboxyl group is ionized and thus negatively-charged at pH 7;
an “acidic” amino acid
very hydrophilic

cysteine
CYS
C

2-amino-3-thio propanoic acid

the thiol group is frequently involved at the active site of enzymes; heavy metals like Hg²⁺ and Pb²⁺ bind to it and inactivate such enzymes; moderately polar and hydrophilic. Often forms disulfide bonds with other CYS in proteins, “locking” them into particular conformations.

glutamine
GLN
Q 

glutamic acid g-amide

the “half amide” of glutamic acid; polar, neutral
hydrophilic

glutamic acid
GLU
E

2-aminopentanedioic acid

the g-carboxyl group is ionized and thus negatively-charged at pH 7;
an “acidic” amino acid
very hydrophilic

glycine
GLY
G

aminoacetic acid

the simplest amino acid and the only one which does not exist as a L-enantiomer. The most polar of the nonpolar amino acids.

histidine
HIS
H

2-amino-
3-(5-imidazole)-
propanoic acid

the imidazole group can pick up or release protons readily at pH 7; frequently involved at the active site of enzymes; one of the “basic” amino acids

isoleucine
ILE
I

2-amino-
3-methyl
pentanoic acid

“branched-chain”
extremely hydrophobic
diet-essential

leucine
LEU
L

2-amino-
4-methyl
pentanoic acid

“branched-chain”
extremely hydrophobic
diet-essential

lysine
LYS
K

2,6-diamino
hexanoic acid

the e-amino group is protonated and thus positively charged at pH 7;  another “basic” amino acid; hydrophilic

methionine
MET
M

2-amino-
4-methylthio-
butanoic acid

the S-methyl group is important in metabolism;  diet-essential;
nonpolar and hydrophobic

phenylalanine
PHE
F

2-amino-3-phenyl propanoic acid

an “aromatic” amino acid
diet-essential;
nonpolar and hydrophobic

proline
PRO
P

pyrrolidine-2-
carboxylic acid

an “imino” acid. the ring prevents free rotation, introducing kinks into protein chains; and there is no NH-type hydrogen bonding when incorporated into a protein chain.
hydrophobic

serine
SER
S

2-amino-
3-hydroxy
propanoic acid

a “hydroxy” amino acid;
the hydroxyl group is frequently involved at the active site of enzymes;
polar, neutral, hydrophilic

threonine
THR
T

2-amino-
3-hydroxy
butanoic acid

a “hydroxy” amino acid;
diet-essential
polar, neutral, hydrophilic

tryptophan
TRP
W

2-amino-
3-(3-indolyl)-
propanoic acid

an “aromatic” amino acid
diet-essential;
nonpolar and hydrophobic, although the ring NH can H-bond

tyrosine
TYR
Y

2-amino-
3-(4-hydroxyphenyl)-
propanoic acid

an “aromatic” amino acid
made from PHE;
nonpolar neutral, although the phenolic OH can H-bond

valine
VAL
V

2-amino-
3-methyl
butanoic acid

“branched-chain”
extremely hydrophobic
diet-essential

PowerPoint-type presentation of info on amino acids and proteins by Warren Gallagher at U Wisconsin Eau Claire are viewable [with Acrobat Reader] at:
http://www.chem.uwec.edu/Chem150_S02/Pages/lectnotes.html  choose #6 
and bookmark the site for future reference