Classifying Amino Acids
In the previous topic we we looked at the basic structure of an amino acid. The figure to the right is a basic representation of an amino acid. Based on the nature of the R side chain, amino acids have defining functions and properties.
A polar molecule is one that has a negative end, with a surplus of electrons and a positive end that is lacking in electrons. these molecules are neutral since the opposing charges offset each other. Water is a polar molecule. Hydrophilic means “water loving.” Hydrophilic molecules are both polar and receptive to water. Hydrophilic Amino Acids bind to and can thus dissolve in water. They have polar or ionic R side chains.
Polar Amino Acids are ones whose R group are alcohol, thiol or amide R side chains.
Basic Amino Acid have amide [NH2] R side chains.
Acidic Amino Acids have acidic side chains.
Hydrophobic means “water hating”. Hydrophobic molecules resist, cannot mix with or dissolve in water. Examples of hydrophobic molecules are oils, fats, and lipids. Hydrophobic Amino Acids has hydrocarbon R/ Side chains.
Non-polar Amino Acids have hydrocarbon R side chains.
Glycine is the simplest stable amino acid. It has a single hydrogen atom as its R side chain.
Proline is the only cyclic amino acid. It does not control the regular NH2 (amino group). The figure to the right shows it’s structure.
Cysteine is unique in that is has a thiol group (sulfhydryl group) as it R side chain. Thiol: [R-S-H].