[[Proteins]] may be broken into their constitutent monomer molecules by hydrolysis. AminoAcid products of the reaction constitute the AminoAcid composition of the [[Proteins]].

 * Standard AminoAcid : 20 amino acids found in [[Proteins]]
 * Nonstandard AminoAcid : chemically mdified after their incorporation into a polypeptide and amino acids that occur in living organisms but are not found in [[Proteins]]. e.g.taurin

These molecules contain a central carbon atom (''alpha''-carbon) to which an amino group, a carboxylate group, a hydrogen atom, and an R(side chain) group are attached. 

At a pH of 7 the carboxyl group of an AminoAcid is in its conjugate base form (-COO-) and the amino group is in its conjugate acid form (-NH3+). Thus each AminoAcid can behave as either an acid or a base. It's called '''Amphoteric''' property of a AminoAcid. Neutral molecules that bear an equal number of positive and negative charges simultaneously are called '''zwitterions'''. It is the R group, however, that gives each AminoAcid its unique properities. Also the pH value that AminoAcid's net charge become zero is called IsoelectricPoint.

=== Names and Abbreviations of the Standard amino acids ===

||'''AminoAcid'''||'''Three-Letter'''||'''One-Letter'''||
||Alanine||Ala||A||
||Arginine||Arg||R||
||Asparagine|| Asn ||N||
||Aspartic acid ||Asp ||D||
||Cysteine ||Cys ||C||
||Glutamic acid ||Glu ||E||
||Glutamine ||Gln ||Q||
||Histidine ||His ||H||
||Isoleucine ||Ile ||I||
||Leucine ||Leu ||L||
||Lysine ||Lys ||K||
||Methionine ||Met ||M||
||Phenylalanine ||Phe ||F||
||Proline ||Pro ||P||
||Serine ||Ser ||S||
||Threonine ||Thr ||T||
||Tryptophan ||Trp ||W||
||Tyrosine ||Tyr ||Y||
||Valine ||Val ||V||

Special AminoAcid
|| SelenoCystein || Sec || U ||

=== Classification of Amino acids ===
 Group I : Hydrophobic  - Nonpolar side Chains
           Ala, Val, Leu, Ile, Pro, Met, Phe, Trp
 
 Group II : Polar, unchanged 
            Gly, Ser, Thr, Cys,Tyr, Asn, Gln
 
 Group III : Acidic
            Asp, Glu
 
 Group IV : Basic
            Lys, Arg, His


=== Properties of each Amino acids ===
♣Histidine(His, H)
 Unique imidazole side chain: effective as nucleophilic catalyst( more basic than hydroxide ion)

 five-membered ring structure --> relatively little steric hindrance 

 pKa = 7

<Aromatic Residues>
 Has UV absorbance and fluorescence properties of proteins.

=== AminoAcid chart ===

{{http://www.ionsource.com/virtit/VirtualIT/chart1.gif}} 

=== 필수 AminoAcid ===

체내에서 합성이 되지 않기 때문에 반드시 섭취해야 하는 8가지 AminoAcid들
 Ile, Leu, Val, Lys, Phe, Trp, Met, Thr