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The monomeric component of peptides and proteins are alpha-amino acids. All amino acids have a similar structure, shown below, and all except glycine can occur in two enantiomeric forms, R and S.
| NAME ABRREV. ABRREV. SIDE CHAIN | STRUCTURE |
| Alanine
Ala
A non-polar |  |
| Arginine
Arg R charged, basic |  |
| Asparagine Asn N polar |  |
| Aspartic acid Asp D charged, acidic |  |
| Cysteine Cys C weakly polar |  |
| Glutamine Gln Q polar |  |
| Glutamic acid Glu E charged, acidic |  |
| Glycine Gly G weakly polar |  |
| Histidine His H charged, basic |  |
| Isoleucine Ile I strongly non-polar |  |
| Leucine Leu L strongly non-polar |  |
| Lysine Lys K charged, basic |  |
| Methionine Met M non-polar |  |
| Phenylalanine Phe F strongly non-polar |  |
| Proline Pro P non-polar |  |
| Serine Ser S weakly polar |  |
| Threonine Thr T weakly polar |  |
| Tryptophan Trp W non-polar |  |
| Tyrosine Tyr Y weakly polar |  |
| Valine Val V strongly non-polar |  |
Amino acids can be covalently linked together by the formation of an amide bond. This bond is formed between the alpha-amino group of one amino acid and the alpha-carboxyl group of the other. The resulting molecule is termed a peptide. Click here to view the formation of a dipeptide by the condensation of glycine and alanine.
The peptide bond, shown below, has some unique characteristics which have a dramatic influence on the 3-D structure of proteins. Due to the partial double bond structure of the C-N bond the amide linkage is planar with little or no rotation possible around the C-N bond.
