Encyclopedia > Amino acid

  Article Content

Amino acid

In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups.

In biochemistry, this shorter and more general term is frequently used to refer to alpha amino acids, that is, those amino acids in which the amino and carboxylate functionalities are attached to the same carbon. Some molecules like proline don't contain an amino group and chemically are not amino acids (technically proline is an imino acid), but are also classified as such because of functional similarity to real amino acids in living cells.

There are 20 amino acide which are directly expressed in the genetic code. If a protein cotains a different amino acide it was modified after building the protein. These modifications are often esential for the function of the protein. Over 500 amino acides have been found in nature.

The generalized structure of alpha amino acids is:

    COOH
    |
  H-C-R
    |
    NH2

Where "R" represents a side chain specific to each particular amino acid. Amino acids are usually classified by properties of the side chain into four groups: acidic, basic, hydrophilic (polar), and hydrophobic (nonpolar).

Except for glycine, where R = H, amino acids occur in two possible optical isomers, called D and L; L amino acids represent the vast majority of amino acids found in proteins. D amino acids are found in some proteins produced by exotic sea-dwelling organisms, such as cone snails. Proteins are created by polymerization of amino acids by peptide bonds in a process called translation:

1. Amino acid; 2, zwitterion structure; 3, two amino acids forming a peptide bond.

Twenty amino acids are represented in the genetic code:

The chemical properties of the side chains are:

Abbrev. Full Name Side chain type Mass Isoelectric point Remarks
A Ala Alanine hydrophobic 89.09 6.11
C Cys Cysteine hydrophilic 121.16 5.05 Two cysteines can form a disulfide bond.
D Asp Aspartic acid acidic 133.10 2.85
E Glu Glutamic acid acidic 147.13 3.15
F Phe Phenylalanine hydrophobic 165.19 5.49
G Gly Glycine hydrophilic 75.07 6.06 Because of the two hydrogen atoms at the α carbon, glycine is not optically active.
HHisHistidinebasic155.167.60
IIle Isoleucinehydrophobic 131.17 6.05
KLys Lysinebasic 146.19 9.60
LLeu Leucinehydrophobic 131.17 6.01
MMet Methioninehydrophobic 149.21 5.74
NAsn Asparaginehydrophilic132.12 5.41
PPro Proline hydrophobic115.13 6.30 Can disrupt protein folding structures like α helix or β sheet.
QGln Glutaminehydrophilic 146.15 5.65
RArg Argininebasic 174.20 10.76
SSer Serinehydrophilic 105.09 5.68
TThr Threoninehydrophilic 119.12 5.60
VVal Valinehydrophobic 117.15 6.00
WTrp Tryptophanhydrophobic 204.23 5.89
YTyr Tyrosinehydrophilic 181.19 5.64

Amino
Acid
hydrophobic positivenegative polarcharged smalltiny aromatic aliphaticvan der Waals volume
Ala X - - - - X X - -67
Cys X - - - - X - - -86
Asp - - X X X X - - -91
Glu - - X X X - - - -109
Phe X - - - - - - X -135
Gly X - - - - X X - -48
His X X - X X - - X -118
Lys X X - X X - - - -135
Ile X - - - - - - - X124
Leu X - - - - - - - X124
Met X - - - - - - - -124
Asn - - - X - X - - -96
Pro - - - - - X - - -90
Gln - - - X - - - - -114
Arg - X - X X - - - -148
Ser - - - X - X X - -73
Thr X - - X - X - - -93
Val X - - - - X - - X105
Trp X - - X - - - X -163
Tyr X - - X - - - X -141



All Wikipedia text is available under the terms of the GNU Free Documentation License

 
  Search Encyclopedia

Search over one million articles, find something about almost anything!
 
 
  
  Featured Article
U. S. state

... NJ New Jersey - Trenton NM New Mexico - Santa Fe NY New York - Albany OH Ohio - Columbus OK Oklahoma - Oklahoma City OR Oregon - Salem PA Pennsylvania - ...