Some amino acids are polar,
meaning that there is an asymmetrical distribution of electronic charge
throughout the molecule. The polarity of amino acids is an important factor
in biological systems because it has a significant effect on how a protein
folds into its active conformation. The amino acid glycine
lacks a side chain and is the least polar in this group. Asparagine
derives its polarity from bonds that contain nitrogen and oxygen atoms,
around which electrons tend to cluster. Serine and threonine
both contain polar hydroxyl groups, while glutamine, like asparagine,
possesses polar bonds containing nitrogen and oxygen atoms. The final two
polar amino acids shown here are distinguished by unique structural features.
Tyrosine contains a planar benzene ring as part of its side group as well as
a polar hydroxyl group, and cysteine possesses a bond containing sulfur,
shown in yellow, another atom with a tendency to collect electrons.
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