<P> Some amino acids have special properties such as cysteine, that can form covalent disulfide bonds to other cysteine residues, proline that forms a cycle to the polypeptide backbone, and glycine that is more flexible than other amino acids . </P> <P> Many proteins undergo a range of posttranslational modifications, when additional chemical groups are attached to the amino acids in proteins . Some modifications can produce hydrophobic lipoproteins, or hydrophilic glycoproteins . These type of modification allow the reversible targeting of a protein to a membrane . For example, the addition and removal of the fatty acid palmitic acid to cysteine residues in some signaling proteins causes the proteins to attach and then detach from cell membranes . </P> <Table> <Tr> <Th> Amino acid </Th> <Th> 3 - letter </Th> <Th> 1 - letter </Th> <Th> Side chain <P> class </P> </Th> <Th> Side chain <P> polarity </P> </Th> <Th> Side chain <P> charge (pH 7.4) </P> </Th> <Th> Hydropathy index </Th> <Th> Absorbance <P> λ (nm) </P> </Th> <Th> ε at <P> λ (mM cm) </P> </Th> <Th> MW <P> (weight) </P> </Th> <Th> Occurrence <P> in proteins </P> <P> (%) </P> </Th> </Tr> <Tr> <Td> Alanine </Td> <Td> Ala </Td> <Td> </Td> <Td> aliphatic </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> 1.8 </Td> <Td> </Td> <Td> </Td> <Td> 89.094 </Td> <Td> 8.76 </Td> </Tr> <Tr> <Td> Arginine </Td> <Td> Arg </Td> <Td> </Td> <Td> basic </Td> <Td> basic polar </Td> <Td> positive </Td> <Td> − 4.5 </Td> <Td> </Td> <Td> </Td> <Td> 174.203 </Td> <Td> 5.78 </Td> </Tr> <Tr> <Td> Asparagine </Td> <Td> Asn </Td> <Td> </Td> <Td> amide </Td> <Td> polar </Td> <Td> neutral </Td> <Td> − 3.5 </Td> <Td> </Td> <Td> </Td> <Td> 132.119 </Td> <Td> 3.93 </Td> </Tr> <Tr> <Td> Aspartic acid </Td> <Td> Asp </Td> <Td> </Td> <Td> acid </Td> <Td> acidic polar </Td> <Td> negative </Td> <Td> − 3.5 </Td> <Td> </Td> <Td> </Td> <Td> 133.104 </Td> <Td> 5.49 </Td> </Tr> <Tr> <Td> Cysteine </Td> <Td> Cys </Td> <Td> </Td> <Td> sulfur - containing </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> 2.5 </Td> <Td> 250 </Td> <Td> 0.3 </Td> <Td> 121.154 </Td> <Td> 1.38 </Td> </Tr> <Tr> <Td> Glutamic acid </Td> <Td> Glu </Td> <Td> </Td> <Td> acid </Td> <Td> acidic polar </Td> <Td> negative </Td> <Td> − 3.5 </Td> <Td> </Td> <Td> </Td> <Td> 147.131 </Td> <Td> 6.32 </Td> </Tr> <Tr> <Td> Glutamine </Td> <Td> Gln </Td> <Td> Q </Td> <Td> amide </Td> <Td> polar </Td> <Td> neutral </Td> <Td> − 3.5 </Td> <Td> </Td> <Td> </Td> <Td> 146.146 </Td> <Td> 3.9 </Td> </Tr> <Tr> <Td> Glycine </Td> <Td> Gly </Td> <Td> </Td> <Td> aliphatic </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> − 0.4 </Td> <Td> </Td> <Td> </Td> <Td> 75.067 </Td> <Td> 7.03 </Td> </Tr> <Tr> <Td> Histidine </Td> <Td> His </Td> <Td> </Td> <Td> basic aromatic </Td> <Td> basic polar </Td> <Td> positive (10%) neutral (90%) </Td> <Td> − 3.2 </Td> <Td> 211 </Td> <Td> 5.9 </Td> <Td> 155.156 </Td> <Td> 2.26 </Td> </Tr> <Tr> <Td> Isoleucine </Td> <Td> Ile </Td> <Td> </Td> <Td> aliphatic </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> 4.5 </Td> <Td> </Td> <Td> </Td> <Td> 131.175 </Td> <Td> 5.49 </Td> </Tr> <Tr> <Td> Leucine </Td> <Td> Leu </Td> <Td> </Td> <Td> aliphatic </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> 3.8 </Td> <Td> </Td> <Td> </Td> <Td> 131.175 </Td> <Td> 9.68 </Td> </Tr> <Tr> <Td> Lysine </Td> <Td> Lys </Td> <Td> </Td> <Td> basic </Td> <Td> basic polar </Td> <Td> positive </Td> <Td> − 3.9 </Td> <Td> </Td> <Td> </Td> <Td> 146.189 </Td> <Td> 5.19 </Td> </Tr> <Tr> <Td> Methionine </Td> <Td> Met </Td> <Td> </Td> <Td> sulfur - containing </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> 1.9 </Td> <Td> </Td> <Td> </Td> <Td> 149.208 </Td> <Td> 2.32 </Td> </Tr> <Tr> <Td> Phenylalanine </Td> <Td> Phe </Td> <Td> </Td> <Td> aromatic </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> 2.8 </Td> <Td> 257, 206, 188 </Td> <Td> 0.2, 9.3, 60.0 </Td> <Td> 165.192 </Td> <Td> 3.87 </Td> </Tr> <Tr> <Td> Proline </Td> <Td> Pro </Td> <Td> </Td> <Td> cyclic </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> − 1.6 </Td> <Td> </Td> <Td> </Td> <Td> 115.132 </Td> <Td> 5.02 </Td> </Tr> <Tr> <Td> Serine </Td> <Td> Ser </Td> <Td> </Td> <Td> hydroxyl - containing </Td> <Td> polar </Td> <Td> neutral </Td> <Td> − 0.8 </Td> <Td> </Td> <Td> </Td> <Td> 105.093 </Td> <Td> 7.14 </Td> </Tr> <Tr> <Td> Threonine </Td> <Td> Thr </Td> <Td> </Td> <Td> hydroxyl - containing </Td> <Td> polar </Td> <Td> neutral </Td> <Td> − 0.7 </Td> <Td> </Td> <Td> </Td> <Td> 119.119 </Td> <Td> 5.53 </Td> </Tr> <Tr> <Td> Tryptophan </Td> <Td> Trp </Td> <Td> </Td> <Td> aromatic </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> − 0.9 </Td> <Td> 280, 219 </Td> <Td> 5.6, 47.0 </Td> <Td> 204.228 </Td> <Td> 1.25 </Td> </Tr> <Tr> <Td> Tyrosine </Td> <Td> Tyr </Td> <Td> Y </Td> <Td> aromatic </Td> <Td> polar </Td> <Td> neutral </Td> <Td> − 1.3 </Td> <Td> 274, 222, 193 </Td> <Td> 1.4, 8.0, 48.0 </Td> <Td> 181.191 </Td> <Td> 2.91 </Td> </Tr> <Tr> <Td> Valine </Td> <Td> Val </Td> <Td> V </Td> <Td> aliphatic </Td> <Td> nonpolar </Td> <Td> neutral </Td> <Td> 4.2 </Td> <Td> </Td> <Td> </Td> <Td> 117.148 </Td> <Td> 6.73 </Td> </Tr> </Table> <Tr> <Th> Amino acid </Th> <Th> 3 - letter </Th> <Th> 1 - letter </Th> <Th> Side chain <P> class </P> </Th> <Th> Side chain <P> polarity </P> </Th> <Th> Side chain <P> charge (pH 7.4) </P> </Th> <Th> Hydropathy index </Th> <Th> Absorbance <P> λ (nm) </P> </Th> <Th> ε at <P> λ (mM cm) </P> </Th> <Th> MW <P> (weight) </P> </Th> <Th> Occurrence <P> in proteins </P> <P> (%) </P> </Th> </Tr>

Table of standard amino acid abbreviations and properties
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