Each amino acid has at least one amine and one acid functional group as the name implies. The different properties result from variations in the structures of different R groups. The R group is often referred to as the amino acid side chain. Amino acids have special common names, however, a three letter abbreviation for the name is used most of the time. A second abbreviation , single letter, is used in long protein structures.Consult the table on the left for structure, names, and abbreviations of 20 amino acids.
There are basically four different classes of amino acids determined by different side chains: (1) non-polar and neutral, (2) polar and neutral, (3) acidic and polar, (4) basic and polar.
Principles of Polarity:
The greater the electronegativity difference between atoms in a bond, the more polar the bond. Partial negative charges are found on the most electronegative atoms, the others are partially positive. Review the polarity of functional groups.
Non-Polar Side Chains:
Side chains which have pure hydrocarbon alkyl groups (alkane branches) or aromatic (benzene rings) arenon-polar. Examples include valine, alanine, leucine, isoleucine, phenylalanine.
The number of alkyl groups also influences the polarity. The more alkyl groups present, the more non-polar the amino acid will be. This effect makes valine more non-polar than alanine; leucine is more non-polar than valine.
QUES. List all amino acids with non-polar side chains.
Rank the following according to increasing non-polarity i.e. 1 = least non-polar, 4 = most non-polar. leu; phe; val; ala
Polar Side Chains:
Side chains which have various functional groups such as acids, amides, alcohols, and amines will impart a more polar character to the amino acid. The ranking of polarity will depend on the relative ranking of polarity for various functional groups as determined in functional groups. In addition, the number of