Structure of Amino Acids

Amino Acids Amino acids are the structural building blocks (monomers) of proteins. There are twenty different kinds of amino acids used in proteins. Proteins are referred to as heteropolymers due the variety of amino acids involved in their structure.

 -carbon

Amino Acids (cont’d.) Amino acids, like carbohydrates, show isomerism. Proteins are only made up of amino acids which are L-isomers. L-isomer D-isomer

Amino Acids (cont’d.) At neutral pH’s amino acids exist in an ionised form and have both acidic and basic properties. This is because the carboxylic group donates hydrogen ions to the solution (acidic) whereas the amino group (NH 2 ) attracts hydrogen ions from the solution.

Amino Acids (cont’d.) The repeating sequence of atoms along a proteins is referred to as the polypeptide backbone. Attached to this repetitive chain are the different amino acid side chains (R-groups) which are not involved in the peptide bond but which give each amino acid its unique property.

Amino Acids (cont’d.) Amino acids are grouped according to whether their side chains are:- acidic basic uncharged polar non polar

AsparticAcidAsparticAcid aspasp D AcidicPolar AcidicPolar Aspartic Acidasp Acidic Polar Glutamic AcidgluAcidic Polar

Lysinelys Basic Polar Argininearg Basic Polar

GlutamineglnNeutral Polar Tyrosine tyr Neutral Polar

Isoleucine ile Neutral Non-polar Methionine met Neutral Non-polar

Amino Acids (cont’d.) The type of side chain is very important as it affects the solubility of the amino acid. Hydrophobic features include long non- polar (uncharged) chains or complex aromatic rings. Hydrophilic features include additional carboxyl groups or amino groups not involved in peptide bonding which are ionised in solution.

Amino Acids (cont’d.) Amino acids link together by covalent peptide bonds. This involves a condensation /dehydration reaction. These bonds are very strong. When this takes place the charged amino and carboxylic groups disappear.