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Properties of Amino Acids


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The properties of α-amino acids are complex, yet simplistic in that every molecule of an amino acid involves two functional groups: carboxyl (-COOH) and amino (-NH2).
Each molecule can contain a side chain or R group, e.g. Alanine is an example of standard amino acid containing methyl side chain group. The R groups have a variety of shapes, sizes, charges, and reactivities. This allows amino acids to be grouped according to the chemical properties of their side chains.

Table of common amino acid abbreviations and properties

Name

Three letter code

One letter code

Molecular
Weight

Molecular
Formula

Residue
Formula

Residue Weight
(-H2O)

pKa

pKb

pKx

pl

Alanine

Ala

A

89.10

C3H7NO2

C3H5NO

71.08

2.34

9.69

6.00

Arginine

Arg

R

174.20

C6H14N4O2

C6H12N4O

156.19

2.17

9.04

12.48

10.76

Asparagine

Asn

N

132.12

C4H8N2O3

C4H6N2O2

114.11

2.02

8.80

5.41

Aspartic acid

Asp

D

133.11

C4H7NO4

C4H5NO3

115.09

1.88

9.60

3.65

2.77

Cysteine

Cys

C

121.16

C3H7NO2S

C3H5NOS

103.15

1.96

10.28

8.18

5.07

Glutamic acid

Glu

E

147.13

C5H9NO4

C5H7NO3

129.12

2.19

9.67

4.25

3.22

Glutamine

Gln

Q

146.15

C5H10N2O3

C5H8N2O2

128.13

2.17

9.13

5.65

Glycine

Gly

G

75.07

C2H5NO2

C2H3NO

57.05

2.34

9.60

5.97

Histidine

His

H

155.16

C6H9N3O2

C6H7N3O

137.14

1.82

9.17

6.00

7.59

Hydroxyproline

Hyp

O

131.13

C5H9NO3

C5H7NO2

113.11

1.82

9.65

Isoleucine

Ile

I

131.18

C6H13NO2

C6H11NO

113.16

2.36

9.60

6.02

Leucine

Leu

L

131.18

C6H13NO2

C6H11NO

113.16

2.36

9.60

5.98

Lysine

Lys

K

146.19

C6H14N2O2

C6H12N2O

128.18

2.18

8.95

10.53

9.74

Methionine

Met

M

149.21

C5H11NO2S

C5H9NOS

131.20

2.28

9.21

5.74

Phenylalanine

Phe

F

165.19

C9H11NO2

C9H9NO

147.18

1.83

9.13

5.48

Proline

Pro

P

115.13

C5H9NO2

C5H7NO

97.12

1.99

10.60

6.30

Pyroglutamatic

Glp

U

139.11

C5H7NO3

C5H5NO2

121.09

5.68

Serine

Ser

S

105.09

C3H7NO3

C3H5NO2

87.08

2.21

9.15

5.68

Threonine

Thr

T

119.12

C4H9NO3

C4H7NO2

101.11

2.09

9.10

5.60

Tryptophan

Trp

W

204.23

C11H12N2O2

C11H10N2O

186.22

2.83

9.39

5.89

Tyrosine

Tyr

Y

181.19

C9H11NO3

C9H9NO2

163.18

2.20

9.11

10.07

5.66

Valine

Val

V

117.15

C5H11NO2

C5H9NO

99.13

2.32

9.62

5.96

Amino acids are crystalline solids which usually are water soluble and only sparingly dissoluble in organic solvents. Their solubility depends on the size and nature of the side chain. Amino acids have very high melting points, up to 200-300°C. Their other properties varying for each particular amino acid.