Types of amino acids:
The twenty or so different amino acids can be classified into three broad groups depending on the structure of the "R" group. This is important because the type of R group an amino acid has determines how it behaves in water. In turn, the amino acid make up of proteins determines the three dimensional structure and the physical and chemical properties of the proteins.
First are non polar amino acids. These generally have carbon and hydrogen, possibly sulfur as in cysteine, but no oxygen in the R group. Two examples valine and phenylalanine:
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Next are polar amino acids. In these amino acids the R group involves polar covalent bonds so that the R group has a positively charged region and a negatively charged region. An example tyrosine. Notice that tyrosine is similar to phenylalanine except that one hydrogen in the R group's carbon ring is replaced by a hydroxyl group.
The last type of amino acids are called ionized or charged amino acids because the R group becomes ionized when the amino acid is in water.* The example here is glutamate.
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* in all amino acids the carboxyl end and the amino end ionize when the amino acid dissolved in water but this is not shown here.
01/23/99 pgd revised 8/7/99