Amino acids are organic compounds that contain carboxylic acid and amino functions. Two amino acids can be joined under suitable conditions, through an amide bond, forming a dipeptide. The dipeptide can incorporate a third amino acid, forming a tripeptide. Chains with more than 50 amino acids are called proteins.

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and Amino acids
The bond that joins the two amino acids to form the dipeptide is called a peptide bond.
Amino acids can be classified as a , b , or g -amino acids depending on the position of the amino group on the carbon chain.
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a -amino acid
b -amino acid
g -amino acid
The a -amino acids are especially important, since the 20 amino acids that form part of the proteins belong to this family. With the exception of proline, these amino acids have the following structure:
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Structure of an alpha amino acid
Glycine (achiral)
With the exception of Glycine (R=H) the amino acids present the asymmetric carbon. It is observed that all the amino acids obtained from (natural) proteins belong to the L series (amino group on the left in the Fischer projection).
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The L-series amino acids have the amino group on the left and are natural.
Amino acids of the D series have the amino group on the right and are artificial.